No sharding, but there is parallelization using write-locks.
Sure, but then:
a) you'll basically never trust a new chain
b) do you have actual reason/evidence that the stakeweight it massively more centralized than it looks, or just a worry?
Anyone can PoS block produce Solana too. Small stakers have a proportional say in blocks, more so than they do in PoW.
It's true the reward isn't based on SOL supply control but it *is* based on ASIC supply control.
Why don't write-locks help?