There's a cruel truth to electing to use any dependency for a game, in that all of it may or may not be a placeholder for the final design. If the code that's there aligns with the design you have, maybe you speed along to shipping something, but all the large productions end up doing things custom somewhere, somehow, whether that's in the binary or through scripts.

But none of the code is necessary to do game design either, because that just reflects the symbolic complexity you're trying to put into it. You can run a simpler scene, with less graphics, and it will still be a game. That's why we have "10-line BASIC" game jams and they produce interesting and playable results. The aspect of making it commercial quality is more tied to getting the necessary kinds and quantities of feedback to find the audience and meet them at their expectations, and sometimes that means using a big-boy engine to get a pile of oft-requested features, but I've also seen it be completely unimportant. It just depends a lot on what you're making.