Well yeah, I agree with you 100%. If you've got a good, well thought-out strategy going on, I don't doubt you could pwn some Ubers. I was just saying that I don't think tiers are important and shouldn't be what prevents you from assembling or battling with the teams you want.
IMO, any team can kick any other teams ass with enough forethought. That being said, NU and UU tiers are kinda like, 'these Pokemon aren't the easiest, so you might want to practice with then a bit first'. I've seen guys use UU and NU in Ubers (actual Ubers, not just noobs who think their team pwns because they have every team member nicknamed some variation of 'God') and hand the team's ass to them on a silver platter with a side of cranberry sauce. It just requires more experience and experimentation than 'O hai mah scizor haz a choise band imma gonna wup yo'.
Few people stick with the tiers. Most teams have a fair mix. UU and NU are simply forcpeople who want to play with the lesser pokemon.