The slashing debuff is an terrible concept. It adds nothing to gameplay, because it's integrated into your base rotations. At the same time, it forces you to run certain comps regardless of whether you want to bring those jobs or not.

The problem is that there are only so many ways in which you can compensate for variations in dps. You can make a job have high personal dps but with little to no raid buffs (like the present SAM and the old MNK), you can compensate for lower personal dps with short duration debuffs (like Trick on NIN), or you can compensate for lower personal dps with short duration raid buffs (like Battle Litany on DRG).

The problem is that on tanks and healers, because we do relatively less damage than dps, it's harder to balance out buffs and debuffs against personal dps. You can't really expect WHM's personal dps to ever really compensate for AST's balance, even if you reduced the damage buff, simply because the damage increase is spread across 4 dps. But if you don't try to offset personal and raid dps, you run into a situation like 3.x WAR, where you have one job providing both the highest personal dps and a mandatory raid dps buff.

Personally, I'd like to see 100% uptime buffs/debuffs go away completely, but I'm aware that the balance is difficult to get right.