I'd say Sinner has decent volleys actually, for the next gen standards atleast.
Also not having finesse is not always an obstacle. Agassi had no finesse but his ballstriking was so amazingly good it made him a contender on every surfaces, every conditions of play.
True, I actually think Sinner and Alcaraz having such contrasting styles is good for the game. Maybe we'll get a Sinneraz slam final next year, we'll see.