This in itself doesn’t make sense, given that when Bardock faces Gas in the Manga Gas comments that Bardock is ABOVE the Low-Class power range (before he even gets the Mid Fight Zenkai), and then Bardock recovers after that fight (logically getting another Zenkai). By all logic Bardock by the time he dies to Frieza should’ve at LEAST been Mid-Class.
Hell, Raditz being “Low-Class” didn’t make sense either when according to Toriyama he shares NAPPA’S rank. Further, he says Saiyans are capable of rank promotions via battle experience, but most of the logic in-verse (such as the beliefs of Vegeta, Nappa, and Raditz himself, just generally speaking), is that your birth rank determines everything. Like, the Saiyan Saga doesn’t make sense if promotions were a thing in Saiyan society.
(This is made especially egregious when you realize Bardock also regained his tail too, which makes Saiyan’s more powerful—Ala OG DB Kid Goku. So he also got a power boost from that as well.) Speaking of, I dunno how he got that back. Allegedly once you lose your tail after a certain level of power development, you don’t regain it because “body adaptations” and you “surpass the Oozaru” (this also doesn’t make sense, it’s a multiplier, but whatever).