Bumgarner isn't even 27 and his velocity dip isn't as severe as Felix's.
Bum is down 1.6 on average and 2.5 off of his top end from 2015. But if you look at his trends, his velocity isn't much different than his early season velo in years past. I think he'll simply heat up.
Felix on the other hand is demonstrating a stark drop. 2.2 off the average and three full clicks off of his top end from last year. The trend is gross too because it's sudden and unprecedented. He's sat 91/92 and been able to touch ~95 for basically the last four years consistently, now he's barely humping it up to 91, all of a sudden.
So the degree of concern for me is much, much higher with Felix. But like I said, he's just so damn good and the pitchability is so high that I think he'll be relatively fine. SP2 fine. Unless his elbow pops or something, which is entirely possible.