One way to answer this question is to compare both ATs as they are right now, and as they will be after this patch goes live (assuming nothing further changes).
Pre-patch: short of a few fringe cases there's no reason at all to pick a Tanker over a Brute. The Brute deals way more damage, is almost as survivable, and is almost as good at managing aggro, and the Tanker gets... a mediocre, non-stacking resistance debuff on a single target that requires cycling their weakest attack to maintain.
Post-patch: short of a few fringe cases there's no reason to pick one over the other. The Brute will deal more damage some of the time, the Tanker will deal more damage some of the time, but there is no longer a clear "this is the no-brainer better choice" problem.