Who decided Rav Moshe is a bigger posek than Rav Belsky? Or than the posek Rav Yankel Shmankel?
We can compare “levels” – in fact, we need to in order to judge who is an authority in the first place! If you can’t comapre levels then how are you to know that someone is a godol? The fact that he is “accepted” as a godol only means that many people have judged his “level” to be that of a godol. But if you cannot compare levels, then these people have no right to accept him as a godol in the first place. And the same common sense that tells you so-and-so stands out among his peers making him an authority, tells you that certain so-and-so’s stand out even more. Or less.
Part of knowing who to follow is to know who is greater. Godol mimenu b’chochma ubaminyan is an assessment that it legitimately made. And as Rav Shach writes – if you dont know who to follow, follow whoever is greater – and, he adds, you can of course tell who is greater.