Since you seem to have much more experience in developing games, I'll take most of your word here. Though from my four years of experience in Unity (albeit at

Since you seem to have much more experience in developing games, I'll take most of your word here. Though from my four years of experience in Unity (albeit at a non-professional level), I was always fighting with the engine when trying to build new things. Trying to build complex UI code using Unity's built-in system was a mess, the serialization system always had weird errors and didn't really work well with version control, adding custom rendering to the rendering engine was full of hacks, and the documentation was quite poor for the more obscure/hidden aspects of the engine up to the point that I was thinking "I can just write these in C++/OpenGL, why do I have to go through all of this crap?". Nowadays I do gamedev at a lesser capacity (and doing more general graphics programming in C++ instead), and since several years ago I haven't really looked too deeply into the engine. I think doing all of these in Unity isn't impossible, just that I'm expecting a lot of friction while doing it. There always seems to be some really good indie developers who are stretching Unity to its limits though (such as Manifold Garden). I always wondered how much they were fighting with the engine to make some specific features.