They are still far stronger than all the other cappers in a combat situation though. At least in a DPS role.
(I mean you've got Sluggas and Mandrakes, and against certain targets Cultists too, who are all good in a combat situation, but due to their melee nature they often won't be putting out as much DPS as Guardians tend to still).
And Mysticism was actually buffed; It now gives you more than it did. Rather, it was Warlocks that were nerfed, needing Mysticism now to grant all their squad bonuses except detection instead of only need it for some.
So Guardians as a whole were nerfed, but not Mysticism.