I honestly don't totally understand the appeal of genning Pokemon excluding competitive battling, (and even then it's very iffy IMO). But as far as collectors, I don't see how genning won't kill the fun entirely. I have several shinies, including a few legendaries that I caught legitimately, and while that was grueling, that's where all the satisfaction comes from. If you just have a box full of shiny genned legendaries, what is even the point?