hm i think it is mostly this way
given some concept of "best" and a set of methods, there exists a ranking from best to worst
people have different concepts of best
it's also very annoying to find said ranking, maybe not that hard but nobody really gives enough of a ****/would be able to get other people to give enough of a **** to actually run tests
the only "data set" that we have are the times people get/record/post online, but those are hardly clean samples to derive conclusions from. the only significant result we can get from these is that something is "possible" (it's possible to sub-7 roux, and it's also possible to sub-7 CFOP). You can't really rule out the possibility of a sub-7 ZZ user on grounds that "it hasn't happened yet" (sorry, we haven't been to mars yet. it's just not going to happen guys. so many people have tried and are even still trying as we speak and nothing's really succeeded. i think our best bet is to just throw in the towel. lol let alone get to the moon, can you imagine how ridiculous a concept that is? i bet even if we had our best scientists working on that we couldn't get th- oh wait ****, nvm)
so when a new cuber comes on and looks at all the methods available and asks which he should choose, the response is that "methods don't have speeds" and that he should "choose the one he likes the most", which is not to say anything about whether or not some methods are objectivity better than others. it's simply a reasonable assumption to make that whoever's asking this question on a speedsolving forum might have a goal of improving his times, and given the difficulty of determining an objective best (or even a concept of best really) the pragmatic mindset to take really is that, of a set of methods like the big 4, it's a much better choice to spend time improving with one method than it is to spend time waffling about choosing the "fastest" one