It's not a bad idea. It certainly would be a buff to 2h tanks, replacing their existing conditionals for the +crit with a single conditional of wielding a great weapon. This has always been the strongest conditional, as although the others can be used whilst SnB, it's a very rare setup where one would use it for a SnB build, where it's almost always taken in a 2h build, making the conditional basically just doing what you're already doing. The other tactics have conditionals that result in some abilities gaining no crit at all as the conditional hasn't been met, whilst this one is always on for all abilities at all times. It would of course mean that the tactic would lose the spirit damage on the channel, which would be a nerf to Chosen, but that could always be incorporated in some other way.
With all that being said, I still prefer how it's done currently. Although it would be a power boost to tanks across the board, it would come at the cost of the individuality and flavor of those classes. I personally much prefer to see classes have stuff tied to their respective mechanics, playstyle, and lore. Provided it's done correctly or course.
For example, If they ever make auras an actual mechanic, I'd love to see the tactic changed to have it interact with the aura system and have the auras be the conditional rather than the great weapon. Something like +5% crit per active aura. Similar to how power of the gods works now.