Sure, let's actually start in reverse. There have been a LOT of WR's who were successful in college without the mass to succeed in the NFL. Guys like Tavon Austin who have simply been manhandled because they were too skinny and despite absolutely elite separation skills, quickness, and speed, were utterly useless at the NFL level. Generally there's a minimum weight/muscle mass of at least 185 lbs. Typically, the taller you are, the more muscle mass you require, which is why someone like Tyreek Hill can get by with less muscle mass than someone like Mike Evans. Davonta Smith is 6'1, which is on the taller side, but he's probably closer to 165 than even 175. Now, hopefully he's trying to add 25 or 30 lbs. of muscle to his frame, but that's a LOT of muscle and probably will significantly affect his speed and quickness. But, without it, he's likely to be manhandled and rendered far less effective as a pro.
Simply put, Ja'Marr Chase at 6'0 and 208 lbs. is a beast who is likely not going to have a problem with the extremely physical nature of NFL CB's, so his game translates to the pros far better than smaller, skinnier guys like Davonta Smith, Jalen Waddle, or Rondale Moore (who is majorly injury-prone). Simply put, if any of these guys could duplicate their collegiate success at the NFL level they'd be absolutely stellar NFL prospects. My preference is for the kid whose physical profile and skill set most reliably projects to the NFL level.
We saw it just last year with Henry Ruggs III, who was the first WR selected, yet was not as good as 2nd rounders who were bigger like Chase Claypool and Tee Higgins. When Odell Beckham Jr. exploded it hailed a victory for the smallish fast WR, but Beckham was 5'11 and 200 lbs. He wasn't really small. Most NFL receivers are at least 190 lbs., and at 200, Beckham was big enough to endure the physicality of the league. Smith is listed at 175 lbs ... and really he's closer to 165 at his Alabama playing weight, which is what you see on film. If Smith could do what he does at 200 lbs., I'd be 100% on board with him ... but the projection is that he can not. Thus we will not see the play that won him the accolades in college.
Ja'Marr Chase's 2019 film is unbelievable, he shows speed and acceleration in pads, run after catch elusiveness, great hands, physical strength at the catch point, good understanding of space in routes and after the catch, and durability. He's strong and thick, so he can make the jump up in competition. It's not that the film of Smith isn't spectacular to watch .... it's just that it's not representative of the NFL. It's a bunch of skinny kids who only spend a few hours a day working on their craft as they grow into their bodies. The NFL is full of guys who devote 10 hours a day every day for years into their craft, and have bodies that are rock freakin' solid of pure muscle, and all of them are bigger and faster than the guys in college ... and in the NFL, they think the game many times faster and more complex and holistically than the kids in college. Defenses are complex and QB's don't have time to let a WR play games vs. a weak CB. Chase can consistently win, giving his QB a window on time within the framework of an offense.
Hope that explains why I'm so high on Ja'Marr Chase as compared to all the other prospects.