i disagree about him not having a weapon - he sees a place where the opponent doesn't cover and clean strikes a ball in there
it is a weapon
How about his return of serve? Check the Tokyo final where he completely dismantled the Raonic serve to bagel him for reference.
His main flaws are his serve (which he should work as hard as possible to improve), his natural lack of power (not much can be done about that and it's not that huge an issue) and how much he struggles when he's forced to defend - in matchups where he cannot take the initiative on a regular basis (Del Potro, Federer...) he looks completely clueless out there; he can't operate from defensive positions as most of his defensive shots land way too short. At his height and speed, he should really look to improve his defensive shotmaking and defense to offense transition imo.