I would almost take that bet. Randle is a better athlete and seems to be able to control his weight. Sullinger's last season with the weight caused stress fracture was Mel Turpinesque.
Better athlete than Sully is irrelevant - he's still not a good athlete (by NBA standards).
Sully is able to overcome his poor conditioning to some degree by being smarter and more skilled than most opponents he faces. His ability to step out and hit the jumper allows him to spread the floor somewhat, his ability to make passes that most bigs wouldn't see helps to keep the defense on it's toes, his variety of post moves allows him to score very effectively in the paint, and he does a good job of using his 280 lbs frame to create carve out space for offensive rebounds and putbacks.
Even though Sully has below average conditioning and athleticism by NBA standards, he does have a strength advantage against most guys he plays against, and he does a surprisingly good job of using his bulk/strength/weight in the post defensively to keep guys away from there spots - he's a difficult guy to move.
Randle has none of those advantages.
I understand you think he will be an above average offensive player in the NBA, but how do you propose he will achieve that? On a matchup-by-matchup basis, how do you believe he's going to beat his defenders?
By using speed/quickness to blow past them?
By using strength to overpower them?
By using height / length to shoot over them?
By using crafty ball handling skills to get around them?
By using his consistent jump shot to help spread the floor?
By using elite IQ and footwork / moveset to outsmart them?
I don't see any of the above as areas in which Randle would have an advantage against the average NBA starter...so how do people predict he's going to score against NBA defenses?
For that matter how many guys can you list from the past decade who have:
a) Had similar physical attributes to Randle
b) Have had a similar skill set to Randle
c) Have become above average starters in the NBA at the PF spot
I've been sitting here for about 15 minutes and I can't think of any. Not one.
Even Carlos Boozer can claim a his long wingspan (7' 2"), dangerous mid-range game (career > 41% outside of 10 feet) above average passing (2.6 assists per 36) and impressive set of post moves (likely helped by his length) as tools that helped him overcome his average height for the position.
Probably the closest guy I can think of is Kris Humphreys - he's had a solid career, but not really an above average started overall. If Humphrey's is Randle's upside, then he's going to leave a lot of people very dissapointed.
Also sorry if my tone comes across as 'smarty pants' or 'taking a stab', that's not my intention. I'm just tying to look at Randle objectively and trying to work out attributes he could make use of to give himself a major advantage in the league, and I just can't think of anything.