I believe that these may not be fully implemented yet. I would imagine since the few T2 skills we can purchase have high memory slot requirements that the higher your skill the less memory slots these will take meaning you will need to invest in both the memory stat and your particular combat skill.
Additionally some of these passive bonuses are far more potent than others by leaps and bounds. (Looking at you necromancy) and people taking these combat skills not to become a pyromancer, geomancer, or necromancer but just to get the passive bonus is a bad idea.
If it were me to combat this I would put those combat skill specific bonuses as talents so you would have to not only invest skill points but also a talent to gain them and these talents could be potent because they would only be accessible by people who invest in that class much like some of the endgame talents in DOS1 requiring max skill in a combat role.
