You can't really tell people not to dictate when no one really has a whole lot of power over our tier lists to begin with. For the reason you said (tiering being based off of usage) we don't have a lot of power over a Pokemon's tiering placement, whether they are deserving of it or not. So we can't really dictate since none of us have a the ability to completely dictate our own tiering system to begin with.
But the fact remains that it's also true that tiering isn't 100% indicative of a Pokemon's viability. A Pokemon can be in a certain tier by usage, but viability wise, they may not be actually deserving of that place. I mean, Pokemon like Donphan aren't good but they're high in usage because they're notorious for being "noobtrap" Pokemon who look a lot better on paper than in practice (despite being not very good in practice). Donphan may be Top 5 in usage but that doesn't mean it's one of the best Pokemon in the tier (in fact, it's one of the worst). The most notorious historical example of this is Electivire in DPP OU who stayed OU throughout the 4th generation despite proving to be an underwhelming Pokemon in practice because it had a lot of appeal on paper for hitting 13 types super effectively. Unfortunately, because certain Pokemon like Donphan are "noobtrap" Pokemon because they're bad in practice, they're going to continue being used highly because they look much better on paper. We don't a whole lot of power over that and even though the issue is much less prevalent today because we've started weighing our stats much more heavily, it's not always going to completely alleviate the problem. Especially in RU, because RU's ladder has been notoriously bad since its inception in BW and especially BW2. We've held on to Pokemon like Sandslash and Ambipom who were totally undeserving of RU status over the past few generations and they were much higher in usage than they "should" have been.
Ultimately, we can't really dictate our tiers, but it's still a key thing to remember that a Pokemon's tiering placement isn't always 100% indicative of how good they are or how bad they are. It's also a fact that a Pokemon in a lower tier can be viable and/or good in a higher tier even if they don't see a lot of usage there. Pokemon like Doublade, Seismitoad, and to an extent Zydog are viable in UU despite not being UU by usage. And a Pokemon can be in a tier by usage, but can in terms of viability not actually deserve to be in that tier. So overall, it's still noteworthy that a our tiers aren't a completely accurate representation of what's viable in each tier, and there are standout cases like Donphan who are RU but not actually deserving of that place (it's probably not going to drop anyways, because it's used a lot on the ladder).