It is true that they are a powerful tool to have but they are far from invincible.
Divekicks are decidedly ground breaking in games where you block by holding away.
Having a block button makes them a lot less potent in itself.
Yang was top 3 in AE, low tier in AE2012, mid tier in USF4. Rufus was never top tier but hes always been good, Evil Ryu divekick is not the reason he is top tier.
For the majority of the IGAU patch supported life, Bladam was definitely not mid tier. I agree towards the end he loss some viability, but I always viewed him as top tier. I suppose Rufus is debatable, but when you watch Glitch use him it makes you think twice about his "decided" tier placement.