If you shard on http2 it will take longer since now it makes multiple ssl connections which have have the ssl handshake.
With http2 it's all multiplexed into one connection. So you have the one ssl connection, but that one connection has multiplexed connections inside it. And since it's one tcp, the tcp sliding window has opened up and is actually faster then opening a new tcp connection.
It does not magically split one connections into many. One domain == one connection. Sure it won't undo your "domain sharding" hacks and merge your CDNs, yeah :)
Those are just ways to lose some of the impact of bloat without addressing the bloat itself.
If you address bloat directly it will benefit all users.