Although, morphling didn't used to get free stats from learning morph, which is the main change that took him from "meh" to "GG they picked morph." His ability to farm used to be anywhere from low to extremely terrible and he was shut down in lane by a number of heroes. Now he just morphs agility at level 3 and has 90 damage, he can just morph strength the second he gets jumped on. Silence needs to turn morph strength off and I'll be happy.
Heroes like Tiny have been huge in the past, and you saw how quickly he got banned in TI2 when he got used again. It's not really about gimmicks, think of it this way. DotA is a giant game a rock, paper, scissors. Currently, the pros have rock down to an art. They both pick rock and they see who can be a better rock. When someone figures out how to play paper, they're going to start crushing rock over and over and over. You think the old rock players are going to start playing scissors? Nope, they're going to start copying paper and trying to simply be a better paper. Trying to come up with new strategies in the middle of tournaments is how you lose a lot of money.
Heroes like Invoker will probably always be huge picks because they aren't really countered. Carries will come and go, however, as will supports. Hybrids are generally just too good at what they do to ever be bad picks by definition. Support carries are incredibly popular right now, but they always will be to some degree, just because the concept of someone who can put out consistent and reliable CC while also doing damage is exactly what you need to do to secure kills.