The trainwreck emoji was in jest in response to
@EBF's second straight week of "train leaving the station!" posts following Deebo Samuel making a play
in the third quarter of preseason games. And these are the first and second preseason games, no less. It's really grasping at hope more than anything else. There's just nothing that's adding up to him being a stud.
- Middling college career?

- Failing to truly stand out amongst thoroughly uninspiring WR competition?

- QB that seems to be regressing by the day?

His high 2nd round draft capital bodes well for him as it relates to opportunities and he does have some plus athletic traits. I think he's a guy that will play in the league for 8+ years, and be solid at that. But I just fail to see the optimism as it relates to any sort of trajectory above "meh" fantasy starter. He's a guy I'd be happy with in the early 2nd of rookie drafts, because I think he's a safe ppr asset. But stud I'm not seeing. Will be fun to watch this one play out.
Nobody said he was a lock to be a superstar. He doesn't have to be that good to provide positive return on his ADP.
This site has him as the #12 rookie pick based on ADP. In the three leagues where I got him, the picks I spent on him were #7, #10, and #17. If he has a solid 8 year career, as you yourself suggested, then he'll likely outperform that ADP. 5 out of my 6 leagues are dynasty, so that's definitely my focus, but let's look at redraft for a minute too.
This site has him as WR66 in PPR. He is
completely unlisted on the top 60 of the three CBS sports analysts. So hypothetically if you are rostering him in redraft then you are getting him near the back of the draft where all you're really sacrificing is a roster spot. The risk is very low that late and the upside is considerable. Even a WR40 finish would be a huge win.
I find your nitpicks to be pretty weak.
1. Middling college career - Deebo had a promising sophomore year, got hurt as a junior, and then came back and had 73.5 yards/game as a senior. That's not going to win you a Biletnikoff, but it prorates to 1176 yards over a 16 game NFL season. It's more than Michael Thomas or Tyreek Hill ever had in college, and more yards/game than JuJu had in his final season at USC. Beyond that, production in college depends heavily on scheme, usage, and supporting cast, so while it's something I do look at, I'm more concerned with the athletic traits and qualities on display. You would've missed out on people like Tyreek Hill, Alvin Kamara, Michael Thomas, and Jimmy Graham if all you did is count college stats. Deebo's new teammate George Kittle had 290 receiving yards as a junior and 314 as a senior in college. Did that tell us everything about his ceiling for the NFL? Stats can tell you something about players, but they are not a perfect gauge for what a player can do.
2. Failing to truly stand out amongst thoroughly uninspiring WR competition - He's only a few weeks into his career and he's made more splash plays than anyone else on the team so far this preseason, so this might be doubly misguided. We know there's a learning curve for the NFL and that many eventual greats struggle to make an immediate impact. From a dynasty standpoint, he could finish the year with 0 catches and it wouldn't necessarily tell us that much about his long-term career. I don't think that's likely though, as they used a high pick on him and have a strong need for playmakers. He will get chances this year, but it might take time. JuJu Smith-Schuster had a great rookie year, and even he didn't come out of the gate dominating. He had zero targets in week one of his rookie year and was gradually worked into the offense. When they called upon him to make plays, he delivered and that led to more opportunities. When they've called Deebo's number this preseason, he has delivered. Why shouldn't people be excited when their guy is gashing teams every time he touches the ball? It's what you want to see and even if it's "only against preseason scrubs" it can still have predictive value. Saquon built his reputation running over amateurs at Penn State and even though those guys were woefully outmatched, it didn't mean his tools weren't real. All you can do is destroy the guy lining up across from you and Deebo has been doing that in the early going.
3. QB that seems to be regressing by the day - Almost completely irrelevant from a dynasty standpoint. You'd love for your WR to be on the same team as a prime Brees/Brady/Rodgers/Mahomes, but a great QB is not required for FF WR relevance and bad QBs don't last in the NFL. If Jimmy G fails in SF, they will try someone else. From a redraft standpoint, Deebo is ranked outside the top 60 WRs and should not require elite QB play to exceed those low expectations. Arizona was the worst passing offense in the NFL last year and they still finished with 2523 yards. San Francisco was middle of the pack with 3867. They may not be the Saints or Chiefs, but there will be some yards and targets to compete for.
Now...do I expect this guy to come in and dominate like Randy Moss? No. To be clear, I don't have him as a can't-miss elite prospect. However, I have him as a top 5 skill position guy in this draft and there are plenty of positives. High draft pick. Special athletic qualities with an unusual size/speed combination. Making plays when called upon and actually LOOKS good on the field so far. Relatively low entry cost in dynasty and redraft. There's a lot to like there. From a redraft standpoint, he plays on a team with bad RBs and only one proven mouth to feed in the passing game (Kittle). I'm not assuming a monster season, but certainly the opportunity to compete for touches and excel is there.