Yeah, and that question that I keep asking myself is… Why should I use unity? And not make my own game engine with a existing API like Ogre or OpenGL? 
I know this isn’t really related to unity but it’s a question I always ask my self when I have just started on creating ap game in unity! Or when I’m almost 2 weeks into the game! I need someone to convince me why I should use unity and not build my own small engine…
And I’m aware building my own 3D engine will take awhile.
Time to market.
If Unity doesn’t provide what you need, then make your own engine.
For learning purposes you might want to make your own engine, but other than that, if an engine is already out there that suits your needs, I would use that.