If someone says "I'm refactoring my game engine", it doesn't mean they're doing a random refactor, it means they're tearing out the guts of the engine.

Now maybe they did do that at some point and are just so blinded that they never thought to deal with the rendering situation, but most likely they did not, because no one prioritized it.

Again, I can tell you're not in the industry so the weird sarcasm thing doesn't work. You're like a kid running around in a diaper trying to sass one of the few adults in the room... it's only going to hit with the other diaper wearers.