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.
If you yourself dont know, then thats fine – not everyone can know the answer to all questions they encounter – but why in the world would you say nobody else can know?
And it’s an error in logic, too, because they themselves compared “levels” of other people! i.e.: “Rav Ovadia Yosef is the leading Sefardi posek of our times.” And how would they know this if you cannot compare him to other sefardi poskim?
And how can one know whether “any of us are on the madreiga of assessing the ‘levels’ of other people” unless you assessed the levels of all those other people who said arent “on the “madgreigah” to do that?
If i were to ask you who is greater – Rav Ovadiah or Rabi Avika — would you say you cannot compare people? Rav Ovadiah or the Rambam? Avraham Avinu?
So clearly, we can compare “levels”, its just that to some, certain comparisons are “obvious” and others are not. Well, to other people, perhaps who are more knowledgable and skilled in assessing these kinds of values, other comparisons are also obvious.