Chaosmancer
Legend
Not a subclass. A stance or a round by round option that can be dropped whenever. It's not like moon druid lost their casting permanently.
If you want to do co-opt another class's reason for existing, you should at least have to burn some spell slots.
Why? Monks don't need to use spell slots to act as scouts, neither do rangers. Bards aren't burning spell slots to have expertise, yet the rogue seems to do fine.
Why is it a bad thing if the Moon Druid and the Barbarian, to thematically tied classes, can both fill the same niche? It isn't like Barbarians can't be given cool things too.
And in terms of "tanking" Barbarian, Fighter, Paladin, Wizard, Rogue, Monk they all approach "tanking" in different ways, but they are all brought up as tanks or off-tanks, so why is it so terrible to add Druid to that list? Heck, Artificers and Clerics can make very good tanky characters too, I've often shocked DMs by how tanky my artificers are.