I also think he will be great but peak is absolutely the wrong term. There are so many things you need to experience to learn no matter how long limbs you may have.Offensively he may struggle a little at times as teams work to scheme against him but defensively I expect him to be at all time great peak level from the get go this year. He is so damn disruptive with his size, length and recovery speed. It's scary to think how great defensively the combo of Wemby and Castle could be in a few years.
Its stuff like positioning, defensive rotations, when to help and when not to, how you operate against PnR at various positions on the court... not to mention learning tendencies and gaining experince on defending the various stars.
Like peak Wemby may be good enough to shut down many of the stars 1on1 but year 2 Wemby isnt gonna do it yet.