@Aretheus
have imagination/a mental image strengen the magic, I think the "I said make me average" is one of the better examples of this, its not saying old civilizations did not know things, but your knowledge of the world does affect how far you can take the effect. The first group of friends being an example, and the healer being another one who thought knowledge of the human body can heal better, but what's required is the mental image.
when did the first person come up with the idea that maybe air is 'something', we had thousands of years prior to that were we had no idea or limited idea, but one person had an thought and proved it and it changes how our world works. its not hard to imagine a world where that thought hasn't happened yet, or where magic is the backbone and such a strong one that the research doesn't go further then 'magic works' imagine fire being easy to make but a wide spread damaging fire being hard due to magic use. how many people would think 'lets find a better way to do this' and never think there may be a better way to cast the spell... I can tell you its a minority of a minority that would think that way, just given video games and how many people minmax, but add onto that no good reason to share info or knowledge, and you have a recipe for stagnation.
@Add1152000
This is the beauty of isekai, the framework is already there to not need worldbuilding, we can assume several things already, im going to take a look at the raws and see, if one of the ways I see this going is right... next chapter is world building, and it seems this story is going more or less how I predicted it would go when mc didn't find town early on, without translation, I cant say for sure if this is going to go the exact way I think. the best way to look at this is the farming isekai for its setting.