Smith's struggles at UCLA have been well-documented, as his weight has kept him off the floor and ineffective when on it. There's little doubt that if Smith cannot get in shape, he will not get significant playing time. Thompson and Howland do not seem very similar in their public personas, but neither has much playing time for players who do not play defense.
However, assuming Smith can get in shape, what kind of player will he be? In his high school days, Smith was known for his touch, soft hands, ability to use his size and surprising quickness. The immediate comparison that comes to mind for most Hoya fans is Mike Sweetney (unfortunately, right down to potentially eating their way out of an NBA career).
Would Mike -- who was a good passer but never racked up assist numbers like the Hoyas' centers usually do -- be as effective distributing the ball? How efficiently awesome would a player like Mike be in an offense that was designed to get him better shots than "here, score against a triple team!"? How many cutters would get easy layups when those triple teams came?
How comparable is Josh Smith to Mike Sweetney? Smith is actually listed as two inches taller, but he looks a bit softer than college Sweetney -- not just in weight but also in pure strength. Still, they seem very comparable subjectively. Objectively, these are their freshman years (Smith stats from kenpom, Sweetney from this post):
Player Min% Poss% Shot% TS% O/D Reb% ARate TORate Blk% Stl% ORtg Sweetney 60% 24% 26% 55% 13/17% 11% 22% 3% 2% 107 Smith 52% 26% 25% 58% 20/14% 7% 16% 5% 2% 110
Darn similar. Smith was an efficient scorer from the go, took a decent amount of shots and was a beast of an offensive rebounder.
This isn't to say (an in shape) junior Josh Smith will be similar to junior Mike Sweetney -- who took a ton of shots, made most of them and was an all-around beast. But Smith was probably the better offensive player as a freshman, and if it really is just the weight holding him back, even his freshman self would be a tremendous add to this team.