Correct me if I'm wrong but the last 5 star running back OSU has had that was a starter was Beanie?
Boom, Saine, Hyde, Zeke, Weber, and Dobbins were 3 and 4 stars and all were studs
There are a couple ways to look at it. Yes, those six were all studs, but per Ramzy's link since 2000 OSU has signed 29 RBs and only three were 5* recruits: Beanie, Clarett, and Sam Maldanado. So the three 5* in 20 years had a 66% success rate, and who knows what Maldanado might've been without the injuries before he ever played here.
That leaves 26 4/3/2* players. Now obviously more than the six you listed were good players, but just using those we'd have a 23% success rate (it's probably closer to 40% if I had to guess). Recruiting numbers don't guarantee anything -- of course lower ranked players can and will turn out to be great. What they get you are better odds. The 2017 class had five 5* players: Chase, Okudah, Wade, Wyatt Davis, and Baron Browning. As of today that's an 80% success rate, and over the next two NFL drafts will likely feature the bulk of our 1st/2nd round draftees (in addition to Fields next year, who was also a 5*).
Now, all of that said, there is likely another trend at work here affecting the dearth of recent 5* RBs at OSU. That's the devaluation of the position nationally, and therefore the overall pool of 5* RBs is likely decreasing. Clarett's class had five 5* RBs; Beanie's class had six. JK Dobbin's class had 1 (and JK was the #2 RB despite being a 4*). Further, the 2020 class had three; '19 had three; '18 had two.
I don't think Ramzy is wrong per se, I just think the context isn't entirely complete. In 2000-2006 maybe JK, Jaelen Gill, and Demario McCall would've ended 5* as well, as they were all ranked #2 at RB in their respective classes. Zeke and Clarett were both ranked #5 RBs in their classes, but 11 years difference likely somewhat impacts why one was 69 overall versus 35 in addition to their respective 4* and 5* statuses. The position matters less in the NFL than it used to, and a lot of these rankings try to base themselves on where these players project into the NFL. So it would make sense the pool of 5* RBs will continue to decrease.