You would see a massive shift away from medieval spear formations and a heavier focus on what we would call Medieval Anti-Armor tactics. In short: Don't try to pierce the shield...hurt them despite the shield.
In the middle ages, most people on the battlefield weren't running around in Full Plate. Full Plate is expensive, time-consuming, and difficult to craft. A full suit of Plate Mail could take months to craft. Instead, most people who were 'armored' wore a simple Breastplate and/or a mail shirt, along with a helmet and whatever arm and leg protection they could get.
So, most of the time, you didn't need to worry about hitting someone in a way that breached their armor, you just had to hit them somewhere their armor was weaker. This (coupled with the ease of training people in their use and how easy/cheap they were to make) is why spears were so popular in medieval infantry formations. You get to stay nice and far away from your enemy and stab at the spots that aren't covered in a sheet of steel.
Where this becomes a problem is when you have someone in Plate. A Plate Mail wearing soldier was practically a dreadnought on the battlefield. Spears, swords, axes...practically any cutting or thrusting weapon melee would just bounce off. For a while, the Longsword was able to penetrate plate with a really strong thrust but as metallurgy got better and plate was made thicker...even that stopped working.
This was the point where, when fighting against heavily armored targets, swords stopped being used on the battlefield. Cutting or piercing plate mail was practically impossible without a polearm (such as the piercing spike on the back of a Halberd) and enough space to swing it. So, you stopped trying to pierce the armor, and you just tried to wreck the guy inside of it without breaking the metal.
Thus: maces, warhammers, and other bludgeoning weapons became the more common weapon used for anti-armor combat. The goal wasn't to penetrate armor, it was to hit someone so hard that it hurt them right through the Plate by transmission of Force. It doesn't matter if your helmet can survive the blow, if your skull experiences a massive enough abrupt change in velocity it will give you a concussion. Hard enough, that might just kill you.
As you have mentioned, the personal shields do not negate forceful impacts. Thus, you would use weapons designed to deliver maximum impulse to your target. This would mean a warhammer, mace, war pick, or other heavy weapon that has the vast bulk of its weight at the striking end.
The goal here, as with dealing with someone in Plate, isn't necessarily to penetrate the shield.If you can, awesome! But, mostly...it's to hit them hard enough that the force of impact is conducted into the body--dealing damage right through the shield.
Armor would still be useful in this case, but it would be...potentially weird.
If you can design armor such that it sits outside of your shield, then you can add bits designed to deflect impacts away from you. Later designs of Plate Mail had features like this to help mitigate the risk of blunt weapons. The human body (and thus, presumably, the shield) lacks these contours, so a blow to your chest would have the full surface area of your torso to hit. If you designed armor that was curved around your chest, then an indirect blow might glance off the side.
If you cannot design armor to sit outside the shield, it may still be useful as a back-up. In this case, armor would still be basically exactly what it was before. Perhaps with a focus on padding and support to try to mitigate some of the impact you take.
In either case, physical shields are still useful. A hit taken by a sturdy piece of wood is a hit not taken by your personal shield. And blunt weapon blows to your wooden shield can be absorbed by the flex of your arm...instead of being taken directly into your body.
Volley Fire from archery weapons would not exist. How reliably heavy archery weapons could penetrate plate armor varies depending on who you ask (and how thick they believe plate armor of the day was). I won't try to go into too much detail here--but we'll say it's theoretically possible for a strong enough bow to penetrate the shield.
The problem is, naturally, the further a projectile flies the more speed it loses. And the faster a projectile is moving when fired, the more drag it produces (equation to compute Drag Force squares the object's velocity). Tests I have seen that show a bow able to pierce Plate has the weapon being fired at practically point blank range (usually within 30-40 feet). Thus, the odds of an arrow maintaining shield-piercing velocity by the time it flies all the way across a battle field in a high arc is practically nil.
In the middle ages, Volley Fire was useful because you could just throw a massive number of arrows at the enemy and, since most of your enemy wasn't wearing full plate--you'd probably hit plenty of unarmored or weakly armored spots.
If archers were to be viable, it would have to be straight-fire at relatively close range (for example, archers atop a castle firing down at invaders at the walls).
In fact, it is questionable whether or not archery would have taken off at all. Early bows would have been utterly useless against shielded targets--so it is uncertain whether or not the development of the Warbow or Heavy Crossbow would have happened at all.
The Lance of a Mounted Soldier was, essentially, the most reliable way to penetrate armor while still maintaining tight formation. There are numerous accounts of blunted lances still piercing through jousting armor which was over-engineered to be as heavy and sturdy as possible. You wouldn't wear jousting armor on the battlefield because it was too hard to move in.
The amount of force delivered by a couched lance striking you, propelled forward by a charging warhorse was enormous. Even if you took an indirect blow and it didn't penetrate your personal shield, it would still knock you over with significant force.
In the same way, as your Personal Shield does not protect you against the force of impact...the sheer blunt force of a Heavy Horse Charge slamming into infantry would still be devastating. Soldiers get bowled over, trampled, knocked into each other, lose their weapons, and so on. It may not kill that many people, but it would shatter your formation and probably terrify any conscripts you had in your ranks (getting run over by multiple horses would be a very scary and deeply unpleasant experience even if it didn't break your shield). If you couldn't get your formation back in order before enemy infantry closed with you...you're history.
Cavalry archers would likely not exist. As you said, a personal shield tanks piercing damage about as well as steel plate. It takes a heavy bow to pierce steel plate--significantly heavier than what you can use from horseback. Chariot Archers may still be viable, if armed with heavy crossbows or warbows...and a Chariot would still do a fantastic job of running people over.
Thus, melee cavalry would still see a lot of use. Even a lighter horse carrying someone armed with a warhammer is still going to make that warhammer hit significantly harder if the rider hits you while he rides by.
This 'personal shield' would also change tactics on the battlefield.
A 'standard baseline' would be established of how much abuse a single person's shield could generally take. You'd then estimate that out based on time in combat, then you'd rotate out troops to put 'fresh shields' on the front line in the same way that a shield wall would rotate troops.
A skilled enough warrior may be able to prevent you from getting a 'straight shot' at him with a blunt weapon. This is especially true if you're dealing with peasant levies or other forms of conscripted troops who have minimal training.
So, your goal becomes similar to how footmen would deal with a Mounted Knight in the middle ages.
Step 1: Put him on the ground. Step 2: Dogpile with weapons.
A similar tactic could be done on a grander scale to allow less skilled combatants to still be effective at fighting. For this, you equip some of your troops with Lucerne Hammers as their 'primary weapon,' mixed in with the soldiers with traditional warhammers and maces.
A Lucerne Hammer has both the hammer on the end of a long pole for massive striking power, and also a hook on the back--which can allow you to catch the legs of an opponent to pull them off their feet.
So, the tactic for these troops becomes: Use the hook to sweep an opponent off their feet, then bring an overhand downward blow with the hammer side. Or simply let your allies dogpile the guy on the ground. Impacts are still a thing, so someone on the ground will have a really hard time getting up if a bunch of people are pounding on them.
Weapons and tactics that maximize impact force are the way to go. You don't need to break the shield if it doesn't negate impact Force. You just need to hit em hard enough that it harms them right through their shield.