I'm mostly speaking to gameplay systems, rendering pipelines, etc. but even then it is quite common in a real gamedev shop to rearrange and replace foundations and guts. And within those off-the-shelf turnkey engines themselves, features are in flux to a far higher degree than other codebases of similar size and complexity.

I thought this post was weird for a few reasons, so I read through your resume, which perfectly explained everything. You're the author of that voxel engine I keep seeing get posted, but you have absolutely no experience in the industry, not even bushleague itch.io stuff. I wouldn't normally call someone out for any of this, but who are you to tell anybody to get grip? You don't even know what you're talking about, which is why your reply is simultaneously naive and a non-sequitur. Chill out. You have a cute toy engine, but it's nothing more than portfolio padding. Until you've actually shipped a real game from start to finish, you've got no room to act like this. A little bit more self awareness please.