That's actually not entirely unreasonable. A DM could restrict his campaign, or even just specific classes, to a certain Tier or Tiers. So, like, the game reaches level 10, you look at the players of the fighter and thief and "have you picked a new character yet?"
Would be a perfect opportunity to add back Prestige Classes, too.
Agreed. One of the mistakes of 4e, I feel, was having class scale all the way to 30, rather than stopping at 10 and having progression replaced by Paragon Path.
Jumping up into a new tier shouldn't simply be evolutionary, it should be transformational.
Jon Snow can't hope to fight against Demon Lords and Ancient Dragons. A Jon Snow who can warg into dragons, and gains draconic strength and stamina even in his normal form, is a narrative that fits what Tier 3 and 4 D&D play should look like.
I mean, what's wrong with fantasy worlds just having a narrative of "Some people are given hidden blessings by the gods. These people can grow in stature, skill, and will from risk. danger and exposure to the evils of the world to grow into people who can challenge the gods themselves".