I agree it's a good one but... when it happens, ok, fantastic. But often is that going to be? Maybe 1/3 battles? And the barbarian won't be targeted/fail their save in every battle, so it's going to be relevant in say, 1/4 battles...
The World Tree ability is relevant every fight - I wouldn't say every found, but saying 1/2 of rounds seems quite likely. So even though it's not quite so dramatic/clutch... it can be. Bamfing a friend out of a very dangerous situation - that too will happen rarely, perhaps even more so than the shrugging off a charm/fear, but it sill be just as impactful.
So you have the same "big clutch" potential, but also a "useful almost all the time" (in combat) side to it, and a small utility one too (climb up on a roof, bamf up the rest of the party up).
So based on frequency and potentcy, the World Tree level 6 ability is better.
It's not just tanking -it's tanking and control