Wow. Is English not your first language?
The sentence structure indicates they're potentially among the best, and could be the best. Not that they are the best.
For instance: "This presidential race potentially could be one of the biggest, if not the biggest, landslides ever" isn't saying it is going to be the biggest landslide ever.
It states it could be a landslide, with the highest potential of being the biggest ever. But never does it flatly state it certainly will be the biggest landslide ever.