You could argue any JUCO transfer comes from a lower league than even Delgatty (especially in the current era, where JUCOs don't get the talent they used to because academic qualification isn't the issue that it was in the Prop 48 heyday). At Alabama, the last time I think we got a small-school guy and hung a lot on his plate was in Saban's first year where Darren Mustin transferred in as a walk-on from MTSU (which at the time had only been an FBS program for 6 years. Mustin started at MLB on Saban's defense and did a really nice job of it.
I'm sure there's someone I'm forgetting but that's the one that jumps out. Josh Cuevas also starting out at Cal Poly (before going to Washington, then UA) is another.
Hot take: I don't think it matters, really. There are a lot of small-school guys that hit growth spurts and by the time they're juniors/seniors, some of these guys are better than what you find at FBS powerhouses. The best example of all was DeMarcus Ware of the Dallas Cowboys. He came out of Auburn HS as a 6'1", 220-pound wide receiver. Auburn passes on him and he signs with Troy, then puts on 3 inches and 40 pounds and becomes one of the best defensive ends to ever play the game.