I disagree: If you summarize the difficulty of all Bitcoin blocks from the chain's tip and you're trying to "rebase" the chain at point x, you'd have to calcula

I disagree: If you summarize the difficulty of all Bitcoin blocks from the chain's tip and you're trying to "rebase" the chain at point x, you'd have to calculate at least the amount of hashes between x and the current tip to display a convincing fork with a similar cummulative difficulty. In proof of stake, since there's no "work" that's connecting the blocks, but just a sortition of who gets to submit a block, this ever growing hash tree doesn't gain more difficulty over time to rebase. That's what Bitcoin Maximalists always cry about and are never able to express in words.