As a straight to UPT guy crossing in 3-4 yr is higher chance than a late rate guy, but the F-35 will eventually normalize just like the raptor. A lot of viper guys have been transitioning lately, and combined with b-courses graduating now, my guess is normalization is only a few years out.
If your ultimate goal is F35, and you're fighting with a desire to fly a viper for a few years first, then I suggest try to get to the F35 now. But, the viper (as an example) is going to be around for a long time, so all is not lost if you don't go to the F35, now or ever. In the end it's the whole "a bird hand is worth two in the bushel" saying...rank your choices based on what you want long term, even if that means you might miss out on your "childhood dream jet" for a few years. I doubt a single dude graduating fat Amy b-course right now really has much, if any, heartburn about not flying a viper, eagle, etc.