1.) Raidbuff value is counted towards the job who provided the raid buff and the metric to compare DPS jobs with is rDPS, which accounts for buffs (i.e. the buff on your personal DPS gets subtracted and added to the buffer instead).
2.) No you would absolutely not bring a job for a 1% dmg difference (which is about 0.125% group DPS if we weigh DPS:tanks:heals as 50:30:20 ratio and assuming the damage values are roughly the same). For such a marginal DPS gain you are better off dropping the extra damage and bring high-impact utility like DPS Raise or group defensives.
Prime example for this: Shadowbringer BLM vs SMN for god knows how long