That's a pretty big tier, late 1st to late second round. I'm not disagreeing with you but that would seem to put him in the Lacy/Bell category (based on where they were drafted) Would you agree with that?
20 - 50 is not some rigid tier I'd carry from year to year, or even necessarily a tier I'd apply to this year. It's a ballpark area where a lot of very good players are typically clustered.
On the general matter of ranking players or constructing tiers, the idea that it would be done independently of scheme fit or need is a bit absurd. Laser focus on one need as preeminent to the exclusion of others is nearly as absurd. There are always several areas of need. One thing you can take to the bank...you're not going to take a player in the first round that you don't project as at least a role player in year 1, and then as a starter by year 2. Otherwise, what's the point? After year 4 he could be gone. There are not enough picks nor cap money to have starter quality players at every position languishing on the bench.
I doubt Gordon would fall to 50 in the draft, but perhaps in another year where no power blocking teams were in need of a running back that might be the case. Also, with the dearth of quality pro style QBs coming out of college, there are signs of a gradual shift toward higher value placed on the running game.
Gordon would be a good fit in Dallas...a power blocking scheme. SF ran a nifty power blocking scheme under the previous regime; I don't know the plans of the new regime. I reiterate, I'd have doubts about Gordon's productivity behind a zone blocking line, and then there are those pesky receiving and pass blocking questions.