Remembering that it usually takes a couple of years for a young big to develop (Jermaine ONeal, Bynum, etc)
Who's "etc"? O'Neal and Bynum are two of the very few big men who showed much "development" after being drafted. Biedrins goes into that category as well. But the overwhelming trend is that if a big man looks poor in his first season, he's not going to amount to anything.
Also, keep in mind that your success stories were very young when they entered the league. Each of them (O'Neal, Bynum, Biedrins) was only 18 at the start of his rookie season. Lopez is 20, so you'd have to compare his rookie year to the third years of the other players:
O'Neal (1999 lockout season): 2.5 ppg, .434 FG%, 2.7 rpg
Bynum (07-08): 13.1 ppg, .636 FG%, 10.2 rpg
Biedrins (06-07): 9.5 ppg, .599 FG%, 9.3 rpg
O'Neal is really the only poster child for true "late-developing big man" in the history of the league, or at least over the last 25 years. He's literally a 1 out of 100 case.
Lopez's ceiling is Anderson Varejao. If he can get close to that, the Suns will have done well.