No Ubers players (who are any good) will agree with you, because they all play Ubers knowing what its true purpose is-- to merely be a ban list for OU.
Ubers is not an actual tier that Smogon has any interest in balancing. It is merely a ban list that people play as if it were a tier, and we have tournaments for it.
Would that not make it it's own seperate tier than technically? I mean if you play tournaments for it, have a more than large enough move pool (of actual contending and apparently slightly more diversity than OU) pokemon able to be used in it, have its own seperate group of players, is entirely different from the other tiers, etc, would that not make it its own tier? If you twist the argument, UU technically isn't a tier either except a tier where things weak too weak to play (or just outclassed) are. Or that OU is a banlist for UU, the real tier and that everyone is playing an imaginary ban list. How would we define a tier then?
The environment is obviously different from UU and OU, Level Cup, NU (which really isn't a tier at all, I mean, who actually plays NU except as specific niches?). In all respects it is a game of it's own so to say it is not a real tier is...well, not accurate. A truer statement would be that "Smogon doesn't have interest in the Uber game and only concerns itself with OU and UU, but mainly OU." (Sounds so elitist, no? But it's true.)
The whole "Ubers is just a banlist" thing was really gone by Gen 3 when it suddenly had enough Pokemon to actually create a team and got Kyogre/Groudon/Rayquaza for weather.