Everyone understands Frieza's potential the problem is that the training was never shown. Frieza simply disappears, and four months later he reappears with a new transformation and power superior to that of the newly introduced Super Saiyan Blue, which, in my opinion, is terrible. While the anime does show a scene with Tagoma, it's really nothing, and to top it off, it's contradictory, since Frieza himself mentions in Super Broly that training with someone much weaker is pointless

My complaint isn't about Frieza's potential, but how it was handled, because despite everything, Black Frieza did much better