Ok. WOW you're wrong.

Let's see...

In my eyes, competitiveness doesn't stem from "using every tool available", but from actual competitiveness, i.e. being able to compete.

I will go over some of the clauses and explain why I think they're HEALTHY and ensure COMPETITIVENESS.

First and foremost, Sleep Clause. Sleep is a frustrating status. It inutilizes your pokémon. You lose up to three turns sitting there, waiting for it to wake up. Without a sleep clause, you have NO REASON not to put every opposing pokémon to sleep. This means you could theoretically run a choice scarfed vivillion with compound eyes and sleep powder, and DISABLE HIS ENTIRE TEAM. You literally strip your enemy of the ability to fight back - the ability to COMPETE.
You know what's the consequence to that? It overcentralizes items. It forces you to run anti-sleep items, anti-sleep tactics, just so you don't fall prey to such a tactic. This, in turn, reduces variability and creativity in teambuilding - you're forced to run an anti-sleep backup strategy, else you're entirely doomed if you meet a sleep-based team.

Then, Evasion Clause. I think you can agree with me that there is little competitive about random chances. Otherwise, we'd see "national slot machine championship" or "annual dice throwing tourney" everywhere. That's what random chances are.
Anything that add evasion (or lower accuracy) are deemed uncompetitive because they add an unecessary random component to the game. Again, they strip an enemy of his ability to fight back - to COMPETE - because what used to be a 100% chance to hit is now a 50% chance, or even lower.
Evasion is unhealthy because it creates uncontrollable situations.
Moody clause is a "sub"clause (despite being showcased as a separate one) due to the randomness it stems. It can also increase the pokémons evasion, which is mostly why it was banned
Additionally, there are only a couple moves that are impossible to miss, most of which are learned only by few pokémon - and they're also rather weak.
There are only two moves which lowers a foe's evasion - and none which sharply lowers it previous to gen VI, either.

Drizzle + Swift Swim: Weather was permanent in GenV (this clause is extinct as of GenVI precisely because of this). As such, you'd be hard pressed to fight a weather team if you didn't have weather of your own.
Swift Swim-like abilities were problematic because it gave its pokémons a free agility as its ability. Swift Swim itself was the worst offender, because not only did it give that, but it ALSO further boosted the damage of pokémons which already had STAB on water-type moves (all pokémon with swift swim are water-types, except for Beartic). Which is why it was banned. Gamefreak itself acknowledged it as uncompetitive, which is why as of GenVI weather is no longer permanent - and why such a tactic is no longer banned on smogon.

The OHKO clause. This one is a little harder to grasp, I guess.
So far, we have gone over the clauses that prevent enemies from fighting back. This time, though, we are talking over a gamble YOU take. Why is it bad? Why can't I do this?
The reasoning I have found, is that it both hinges on excessive luck, AND if it does work, it ensures a kill you might otherwise not "deserve". Say you have a specially offensive pokémon, and your enemy has an eviolite chansey up. If you're not aware, eviolite chansey is pretty much the "best" special wall in pokémon. Seriously. 255 base HP, insanely high sp.def + eviolite boost, and has seismic toss, toxic, and softboiled. What's not to love?
So, then how do you kill it? Well, you switch to a physically offensive pokémon (preferrably with fighting stab).
If you use a 1hko move on it with your special attacker, and managed to hit, you then get a kill you should not have gotten. You have slain in one move a pokémon meant to live through at least two moves it is most weak to (a Mega lucario BARELY 1hkos it with Close Combat - yep, that's right).
I hope you got my point. If you didn't, that's fine.

Now, as far as tiers go. YOU ARE ALLOWED TO USE ANY POKÉMON FROM A LOWER TIER. You CAN use a pokémon from UnderUsed (UU) on OverUsed (OU) teams. I myself seldom make a serious team without Florges and/or chandelure despite they being UU. Tiers are NOT created solely based on power. There's more to them than that.


In conclusion, I think you need to check what competitive really means. Most of all, you should learn the meaning of overcentralization.
A healthy competitive environment is one that stems creativity all the while maintaining as fair of a ground as possible. This does mean banning a few pokémon or tactics that aren't officially restricted at all.

PS: Where does Smogon say they're official? There isn't a single mention anywhere in their sites.