I agree with most of what KerrAvron2055 said, especially with the "shield wall" vs. "scattered film-duels". Side note: if you moved way further back in history (early bronze age), before tight shield-wall formations became a thing, it might be quite interestingly different though! I'm going to go with the percentages you gave for the general population (1 in 20 and 1 in 10,000, resp.), but I imagine that these people would be more likely to end up in the army, so these percentages could go up quite significantly. I imagine that 1 in 5 and 1 in 1000 is not a very unrealistic guess!
These "superhumans" would certainly change the tactics used. Several options arise in my head. Thinking this way: the major jobs of a spearman in a battle would be to harass the enemy directly opposite, defend themselves and their comrades immediately left and right, and to look for openings in enemy formations diagonally. If your army has 5% +10s, you could put, say, 4 rows of infantry, where every 5th in the front row is a superhuman - he can easily defend himself and 2 people on each side, while dealing some good strikes into the opposing line. If your enemy doesn't have any +10s in their formation, they can have 20 rows and will still lose.
Or some other general can have a completely different idea - why not combine the 5% of your +10s into an elite unit (possibly with the +20s on corners or the spearhead), which would have no trouble outflanking the enemy formation and smashing their flanks, very likely causing the army to rout!
OK, you might say, but large-scale battles were rather rare. Most fighting was done in sieges and small-ish skirmishes (KerrAvron2055 mentions this in his answer). Well, one of the major uses of heavy cavalry, such as medieval knights, is exactly that - skirmishes! They would keep bothering, annoying and weakening the enemy force as it marches, tries to get some food or firewood, very much a wolf-pack hit-and-run tactics. So why don't make your 5% +10s an elite cavalry unit with the best horses you can get your hands on, to just never give your enemy a moment of peace, kill their lumber parties, attack their supply wagons, crush any smaller detachments, and just disappear in a cloud of dust when being overpowered?
Similarly with sieges. I agree that "Special individuals... are not powerful enough to sally forth and break through a besieging army." But when you have a besieged city with, say, 1000 defenders, then you can make a sortie with a unit of 50 elite heavy cavalry, and even though they likely won't make a dramatic breakthrough, they might be able to inflict some solid damage to the enemy army - which is often not in a great shape to start with! On the besieging side, you probably wouldn't see a +10 unit charging with ladders only to be shot down, but they could still either 1) spearhead any attack after ramming the gate / putting up towers / breaching the walls or 2) exploit any stratagem of war such as infiltrating the castle/city as civilians or sneak in via a path open by a spy on the inside.
Anyway, my point was that beyond this simple "mix or split" decision there are an infinite number of alternatives, and a good tactician might use one or another based on the circumstances - it would definitely change the scene noticeably.
NOTE: This was all assuming that both parties would have a similar proportion of these superhumans. In case one side did have them (5% +10s and a handful of +20s in a large-ish army) and the other side didn't, there might not even be all that many fights happening! Are you going to go in a war with a power whose front line you can't break through in a battle and where you can expect at any time having one of both of your flanks smashed with ease? If you are - your soldiers won't be very happy to fight for you. Think of a "weapon push" (can't find a good link, can only recommend Murray's War Games - when your opponent has superior equipment, your troops are less likely to fight and more likely to run or surrender), but with "weaponised" superhumans. Reputation can do A LOT - think Swiss pikemen, which could march at you in a way to make soldiers run even before any physical contact happened, or Hussite rebels with their enemies taking flight upon just hearing their battle hymn.