As Waifuu stated, it depends on your power, and how well rounded your refinements are. Also take into consideration that what you put towards 4 starring him could also be used for possibly another meta heavy ninja. Personally, due to his revive, I wouldn't ever 4 star mine unless I managed to get lucky with an 80 frag drop of some sort. Hopefully someone who has him 4 star can give you some insight on this.

He isn't "useless" per say. He's still very much endgame. The situation here is that it may be better (depending on the person) to invest in future ninjas rather than one you may use only situationally down the line. DPH will always be viable and good at what he does, but you also want to have a variety of ninjas, especially with high BP for war, spacetime, etc. If anyone has the resources to 4 star a ninja then I say go for it. I avoid doing it because, yes I have a ton of event ninjas, but I cant use them all, so for me 3 stars is perfect and always have a variety of comps I can run for counters, etc.