I main ninja and use it in Eden Savage. Ninja is honestly fine for casual content, I'm not even sure if it lags in dps for aoe dungeon mobs (if someone knows more please share) and player skill in non-savage/extreme creates way more of a gap than at most a 10% difference in dps if everyone were playing optimally.
In savage it's the worst of the four melee in terms of raid dps (this includes Trick Attack). There is zero reason to take a ninja over monk/dragoon right now which are the meta melees, all else being equal. That being said every class including ninja has cleared E4S at this point so if you can play well you're fine, you just won't be able to carry your party like if you were a good monk or blm. Another issue though is locking out classes in pf, since dps checks are tight right now in E2S+, I've seen quite a few clear parties on Crystal locking out ninja (for some reason they never lock out dancer or rdm though, even though they have even lower rdps).
Ninja needs a boost in savage for sure, especially considering how they're the least popular class in that content by a significant gap. Luckily the team has acknowledged the problems in the live letter and changes are coming in 5.1
