@Liquidxlax I mean any world with any level of travel above 0 is going to get mild isekai pollution.
@Ovdose When looking at these fantasy worlds you also need to remember that technology and advancement in general is not a linear process. You don't just age of empires yourself in stages going by years. Its actually more expected to see variance in the evolution of societies in all manners with the only universal points being related to common resource and other general requirements to achieve said advances or idea's. Japan showcased this well with Katana's which are masterpieces for sure. They only exist out of necessity thanks to the poor quality of a material requiring creative solutions. They made a weapon and method so different from everywhere else not because of any tech level or advanced culture but because it was the best option available.
In these fantasy worlds simple things like cow tags and chocolate bars could come about easily before they did in our own world or not at all. There are many cultures which were more advanced in various ways than each other. Advances in a society for instance doesn't require any specific tech level until you get into quick mass communication over distance. You don't need to make a sword or tell the time to have intricate laws and social conventions. Just like you can make sweet weapons without ever wondering if "equality" or "fairness" might be a good idea. Sure they all play off each other but its entirely possible to create a gun before you figure out agriculture. Unlikely but possible.
Sorry if this turned into a big thing but a lot of people like to pull out calendars and age of empire progression as if the path their specific society has taken is the only one. The levels do exist but its not as small as cow tags or rapiers. The things that are red flags are plastic pill bottles with screw tops and pressed, clearly mass produced pills inside. You can get away with some of that but there are certain requirements to make something like that which are implied upon its introduction. You now have to figure out how they are producing the materials alone while still relying on much less effective techniques in every other way. Usually you end up assuming "A wizard did it" because nothing short of magic could explain its specific nature.
So i leave this here for any who would fall into such a trap as to think technology and societies are bound by our own worlds standards and timescale. The truth of the matter is that entire branches of advancement have been lost time and time again without us ever knowing it. A village that figures out complex mathematics but didn't have swords could be easily killed by those with swords and forgotten to time. History is too patchy to be trusted. You almost have to assume your missing pieces while you put together what you do have, no matter how good a picture it paints.