Setting: 4 types of magic, namely bio, godly, Ancient and artifact.
Bio magic: throwing fireballs, making things float, destroying household items seemingly defying you on purpose...
- Relatively weak, invokable by any human (usually) but it is quite taxing.
- Effects in the order of "make 200kg float".
- Requires training and a decent load of talent.
- Mostly used domestically.
Godly magic: weather, landslides, pregnancies...
- Powerful and indirectly invokable by humans.
- Humans pray to a deity, deity checks their mood, humans rejoice/cower in fear/nothing.
- Effects are in the size of our natural disasters, earthquakes, minor hurricanes, overnight harvests.
- Deities are of the ancient Greek kind: fickle, vindictive, prone to playing favorites, etc.
Ancient magic: Time, Life, Fate ...
- Power is almost limitless but uncontrollable.
- No specific way to gain its favor or invoke its wrath.
- Effects are in the order of "surviving after being buried in molten lava" and such miracles.
Artifact magic: any of the 3 preceding types of magic can become bound in an artifact.
- This makes it less powerful and fleeting but changes how it works.
- It responds semi-stochastically to certain magic inputs that humans can produce.
- For the current question it can be considered as reliable as medieval as alchemy. Sometimes it heals, sometimes things blow up and sometimes you are left with just the stuff you started with except now you look like a muttering fool.
- Imbuing can only be done by powers capable of invoking the magic.
- Artifacts of bio magic are generally very weak, except for those with a strong natural affinity for imbuing and a talent for magic.
- Artifacts of godly magic are rare but powerful. Generally not capable of natural disasters they are powerful weapons of war, breaching walls or damaging ports with tidal waves.
- Artifacts of Ancient magic are the stuff of myths: capable of resurrecting the dead, bending time to the owners' wishes, allowing you to overthrow a deity. Many young fools have gone out in pursuit but none have managed to recover such an artifact.
Most magic infused worlds are in 1 of 2 situations :
1) magic is public and the world is medieval consisting of several medium/small kingdoms, possibly of differing species.
2) the world followed our history with its monsters, heroes and creatures capable of wielding magic kept themselves hidden throughout all of it.
At first, it seems strange that so many worlds would get stuck in the Middle Ages but it's not: in our history, it took the positive side-effects of the Black Death to get us going. Damaging the absolute rule of the church, infusing the survivors with greater wealth, killing ruling dynasties. The increased scarcity of labor improved quality of life and increased demand for better agriculture. This led to trade and independent cities along trading routes. Guilds, crafts, bourgeoisie and the seeds of the Renaissance were sown. Any magic society that could wield healing magic, would be far better suited against a virulent disease. Healing magic is always practical and will, therefore, be honed, allowing greater survival odds. Corpse infection would also be out of the question since a few household fireballs could incinerate a corpse beyond danger.
Without such a monster plague to shake up the status-quo, could a magic society ever get to a continental level? With ruling families controlling powerful artifacts, uprisings are easy to strike down but large areas of influence are hard. You can't really give a representative a powerful, irreplaceable weapon and expect them to continue to obey you without question. They have leverage and eventually, a representative will try to leverage that into a land of their own. On the other hand, it is very hard to control peasants without a powerful deterrent, if you have come to rely on it. Suddenly training a military capable of holding a region in check is costly and requires logistics that are a step above regular govern-a-few-dozen-peasant logistics. This would deter would-be conquerors since it would take a lot of effort, which most despots try to avoid.
Such a situation looks like it would stall in a constant cycle of rise and fall of lineages fueled by a few handful artifacts collecting dust as a deterrent until the current owner gets overthrown or the line dies out every couple of centuries (or decades). Since there would no trade, rulers would be content with every pair of hands working the fields barely providing for themselves and providing royally for their liege. Long distance travel would be non-existent except for the few travelers brave and stupid enough, wielding some bio artifact powerful enough to protect themselves and weak enough to not get confiscated on arrival at a castle (bored greedy kings are usually looking to increase their amount of dust-collectors).
The issue is not technology. The aspect of interest is the sociological part: empowering the peasantry, independent cities, free trade. The assumption is that the situation of many small kingdoms has already manifested. Could such a social situation be broken from within or would some great natural disaster be needed to get things going?