Glass. It’s all in the glass.
Ever wonder why that killer zoom doesn’t take great pictures?
Two reasons. Crappy glass and low light.
Now, you need good optics to capture reality, at all close to what the eye can see, and at all aesthetically pleasing.
Without good optics, the best camera in the world won’t shoot diddley.
Second, you need sufficient light to hit the film or sensor. Else you wind up with not so good shots and maybe even need artificial light which typically is another source of bad shots.
So, first things first.
Good optics can compensate for not the best camera and make the great cameras what they are meant to be.
Glass. Its the glass.
Did I mention quality optics allow more light?