I think the tanks are OK as is with two things that could be improved upon.

The two issues I see are that tanks function best after the 64-66 level skills/traits are obtained, because their skillsets are designed in such a way that only with the skills from levels 66-70 does everything begin to fall into place. So in pre-60 content especially, the tanks can feel clunky because they just don't work as well as they used to.

Second thing is Tenacity. Square Enix, you added a role statistic and then made it's impact almost negligible. What were you thinking? Why would anyone stack their role stat if it has next to no appreciable impact? Fix that. The whole STR/VIT damage scaling thing would be moot if Tenacity had a decent impact; especially as significant impact with Tenacity also boosts healing and damage resistance.

Significantly better impact from Tenacity would grease the wheels of the clunky design in pre-60 content since it lifts tanks in 3 key areas and makes a virtue of stacking something besides STR.