Yeah, I think that's the important context here. This stat basically measures how good a player is once he has the ball at his feet – resisting pressure, carrying the ball and beating opponents – while also taking the difficulty of those actions into account. And in that very specific area, Saelemaekers apparently is genuinely elite. Statistically even the best in all top 5 leagues lol.
The problem, as you said, is what happens afterwards. He can beat his man, escape pressure and carry the ball into dangerous areas, but his final pass and finishing aren't anywhere near the same level.
Then again, if Saelemaekers combined that 93.6 on-ball ability with elite key passes, assists and goals, he probably wouldn't be playing for Milan. He'd be at City, PSG or another club paying €100m for him.
So I think the stat actually describes Saelemaekers quite well: exceptional at getting somewhere with the ball, considerably less exceptional at deciding what happens once he gets there.