I enjoyed Legion but I got the legendary I wanted fairly early and that was probably the GOAT era for subtlety in PvE doing that mid-air dance DFA combo with crit shoulders. So I would rank TBC first, then Wotlk and Legion equal (both good but flawed) and everything else a fair way below them.
I think a lot of Shadowlands success is purely because it's better than BFA. If we compare it in isolation to older expansions it's not very good.