Why do you think it's going to take "a few years"? The other top picks are the same age. Actually, Cade and Green are 19 and Mobley is 20.
Mobley is a pretty skilled player from everything I've seen and read. He was an extremely accomplished college player who played in a major conference.
Only [Anthony] Davis accomplished what Mobley did as a freshman, taking home conference Player of the Year, Defensive Player of the Year and Freshman of the Year honors in the same season. Since Box Plus-Minus was introduced to the college game, only three players finished with a better mark than Mobley: Davis, Zion Williamson and Karl-Anthony Towns. Mobley also led the NCAA in Win Shares this past season, thrusting USC into the Elite Eight for the second time in two decades. - Chris Fedor
It's not like he played in a small conference like Windler or is considered "raw" like Kuminga. He's not an 18-year-old international player like Giannis was when he was drafted. Mobley seems prepared to make an impact immediately.
I could see him having a rookie season similar to Okoro last year - more of a defensive contributor than offense, but like Okoro his offense should pick up in the second half.