Any chain that's running under one second block times is probably doing something funny to get around global network latency. As an example, EOS did a sort of workaround by having a single node generate 6 or 12 blocks consecutively (I forget which it was) in order to be able to advertise 500ms block time.

Also, note that speeding up block production in this way usually doesn't tend to speed up the number of transactions a blockchain can handle: it's mainly of benefit for latency (the blockchain rules can react a little quicker to transactions that are generated by users, since the a newly generated transaction doesn't have to wait quite as long for the next block that can include it).