Honestly, it’s not THAT bad. One of my hobbies is to evaluate the source code of as many engines as I can. (Yeah, that sounds weird, but it’s true – I’ve paid for MANY engine licenses over the years!)
Every engine is going to have a bunch of code that is driven by shipping pressure, rather than ivory tower computer science. That’s OK. That’s how real work gets done in the real world.
I think the engine that had the least compromise was the C4 engine. However, in the end, that business model didn’t work out for the creator of the engine, and honestly, while the genius of one dedicated engineer can go far, it can’t go as far as the collective efforts of hundreds of people over time.