From my Knowledge VS started out as a Minecraft mod but quickly hit the games limits. So, I'd argue that VS is a mod turned game. Not quite an engine nor a game on its own. I'll add that VS does seem to encourage modded playthroughs. And anyone who has toyed with the gunpowder mod knows that last section becomes much easier albeit still unforgiving. I am very new to the game still at the point of watching tutorials for everything I do lest I destroy hours of progress haha, so feel free to correct me