Had to look up 'progression fantasy'. So it's basically like a niche genre that uses more or less the same structure as Dragon Ball Z (characters getting progressively more powerful over time)? Or am I misunderstanding it?
In a sense, yes. I read a good number of works that overlap with the "progression fantasy" genre, and I'd say they have 3 main characteristics:
1. Fantasy. They have interesting and engaging fantasy worlds. There's a lot of mixed results here, I personally don't think DBZ or Cradle are that interesting.
2. The main characters are empowered to actively participate in events that surround them. The trope here is that they fight back against the latest unfairness of the world, but more creative storytelling can make this very fresh and interesting.
3. The main characters aren't defined by their circumstances. They prove themselves by their work ethic or cleverness, not by being born to a powerful family.
Most works in this category are rehashes of CRPG or Xianxia tropes. I'd personally recommend Mother of Learning as the best progression fantasy I've read.
Yes. I'm not sure about GP's point that it never would have survived under the old model either. It's a pretty common trope in Wuxia, one of the oldest genres of literature still active today.