Bucky is a perfect example of people paying too much attention to underwear measurements and not actual football skills. Everything we see from him now is what he did in Oregon. Dude has always been a missed tackle stud.
F 'em Buc!
I liked his NCAA clips, but the biggest issue for me was him being 5'9" 192. On some level the measurables do matter. I compared him to Gio Bernard going into the season. Thus far his efficiency is blowing Bernard's first few years away, so it seems like I underestimated how dynamic he could be, but there's still a question of whether he's a complementary type or someone who can handle high volume. 192 is not the weight you want to see in a workhorse type of back.
Him getting banged up immediately after his first game of 15+ carries is perhaps not the victory lap some want it to be.
Now if we want to think of guys who had lasting success in that size bracket, there are some possible good outcomes. Warrick Dunn had a similar build. Ekeler is not much bigger. Chris Johnson was skinny. I'd argue that Ray Rice had a lot more thump than Irving, but on paper 5'8" 200 doesn't look much bulkier than 5'9" 192. I don't think it's impossible for a guy with these dimensions to be long-term relevant, but workload limitations are still a looming threat IMO, even if his talent is legit.
Jamal Charles, Devon Achane and Jamyr Gibbs are a few more in this size bracket.
Agreed it's not ideal size, but the days of the bellcow are mostly over. These smaller, hyper efficient per touch guys that can make people miss will probably begin to populate the 'starting' RB pool as much as the prototype 5'10 225lber does.
Days of the bellcow are not ending as long as guys like Henry, Saquon, and Jacobs exist. Look at this year's top FF backs.
Charles, Achane, and Gibbs have elite track speed. Same for Chris Johnson. Irving ran a 4.55 at the combine. I don't feel as comfortable betting on a likely low volume back if his underlying explosiveness is not as elite. The possibility to compensate for low volume with chunk plays is not as strong. Irving ranks 28th in the NFL in carries and T-12th in explosive runs, which is moderately impressive, but not necessarily indicative of special big play flair. If he's a 5'9" 192 pound grinder then it's probably not the blueprint for enduring FF dominance. I'd lean towards people like Ekeler, Dunn, and Kyren as being his absolute best-case outcomes.
That's a good ceiling for the entry price, but there's also the possibility that he backslides ala Ameer Abdullah, Gio Bernard, or Julius Jones. There's a tendency when rookie backs flash talent to assume that the arrow always has to keep moving up and that the small sample size will always generalize to the rest of their careers. In reality it's not always that smooth, so if you are locking him in as a bankable dynasty commodity based on half a season of split duty then you may be setting yourself up for disappointment.
I don't disagree with the majority of your post, but re: true bellcows - 2/3 names on your list are hall of famers. How many guys drafted in the last 4-5 years have been drafted with the intention of making them the true primary back? Breece, Bijan and maybe Najee? Of the prob dozen or so teams in the league that are employing 1 primary back, how many of them actually 'want' to be? I don't think NO or LAR are thrilled they havent been able to take more off the plate of their guys. CMC (another potential HOF) has probably seen his last days as a true bellcow after a season of what looked like an accumulation of overuse finally coming home to roost.
I think the devaluing of the position cap-wise and draft-capital wise has opened up the committee approach for most teams. Add to the the gradual rule changes being made to give the offensive players more space, and its no wonder you are getting some smaller guys at both RB and WR that are able to have a pretty significant impact on games.
As far as Bucky vs the previous 3 names I mentioned - yes he may not have the underwear speed that they do, and that probably won't equate to the amount of 60+ yard runs those guys tend to pop off, but (especially based on your own numbers) I think the efficiency at which he creates explosive runs shows he's "fast enough" and has the vision to find holes consistently to create the chunk plays you're looking for from your "lightning."
Not sure how many took him where he was going with the anticipation of him becoming a bonafide number 1 primary back, but the sample size we have thus far is showing that much like some of his smaller RB compatriots, he may not need that to be a fantasy asset.
I also don't believe for a second that the listed weight of a 22 year old at 192lbs means he's going to be 'undersized' his whole career. You aren't close to physical maturity at 22 years old. Not by a mile. If this guy wants to/its deemed necessary for him to put weight on, he will have 0 problem working his way up to the elusive 200lb mark while having no negative impact on his explosiveness (in fact I'll argue it might even help his speed).