I wish Gunbreaker would be a DPS class.

[Seraphor]

Sure, so either way, a slashing debuff from gunbreaker won't do anything to the meta (by itself).

There’s currently a 33% chance that your tanks won’t have the ability to apply any slashing debuff (PLD/DRK) that makes having a NIN or a SAM more important.
Now that half of our tanks will be able to apply a slashing debuff (WAR and GUN) that NIN and SAM will be less essential.
While this might be a mark down for the somewhat neglected SAM, it’s a bonus against the essential inclusion of NIN.