I don't see why Farley is seen as so "boom or bust" or "one hit wonder". He had a pretty good freshman year and a really good sophomore year, so he's put up 2 years of quality tape. Micah Parsons has a similar story, and no one calls him a one-hit wonder. Ja'Marr Chase only had one year, and no one questions him as a top draft pick.
The injuries are a big risk, but Farley's already shown the mix of tape and athleticism that you want to see in a high first rounder. There's a lot he's proven and not much to project.
Surtain makes Farley look risky by comparison, but it's more that Surtain is super, super polished than Farley really is some kind of athletic gamble pick. Surtain started 3 out of 3 years at Bama, won the Jim Thorpe award this season, allowed virtually no yardage, committed literally zero penalties, I don't think he ever missed a game with injury... his college resume is sparkling. It's difficult to even find ways to make it better.
People tend to lump Farley and Surtain into this "safe guy/gamble guy" dichotomy, but it's really more like "safe guy/super safe guy."