> The fact is that a single person with a decent amount of knowledge can write a game engine that is more or less complete, while not even FANG companies can write a web browser from scratch should definitely be proof that the latter is more complex.

Again you're trying to backtrace the results to the complexity of the task and the linkage simply does not make sense.

> Some physics and linear algebra, while I’m not saying is easy, but it is not a complex layouting and CSS engine, with a state of the art language runtime, with all the possible requests, sandboxing, etc. — of course you don’t necessarily have to write an optimized browser, but still, just implementing a usable subset of the web is ridiculously hard.

Well it seems to be easier because you can literally look it up through the internet and implement it as a set of rules. The hard part would be the combinatorial number of cases. If you don't have the math requirements to make a game with a 3d world from scratch it will not feel good.