Polygon right now has capped the number of validators at 100, and the protocol atop which it is built (Tendermint/“Peppermint”) only remains fast and cheap if the “active set” of validators remains small. Polygon team have said they will introduce an “auction” mechanism for new validators to join the active set, but one would anticipate that will just favor validators with large stakes (i.e. the existing validator active set). Cosmos/ATOM is the sort of keeper of Tendermint and responsible for the reference implementation and they too cap the validator active set at 125 or 130. Practically speaking none of these L2s are very decentralized. They are fast and cheap which is what most people want but practically pretty centralized...(i.e. project founders and early operators are totally capable of launching 50% or 2/3rds attacks...they probably just don’t want to, and the small “active set” of validators is likely to mostly stay the same). A genuinely decentralized PoS L2 (i.e. can accommodate very large number of validators) that is also fast and cheap is something I’d love to see