Hm, just thought I'd add my two cents on this one, because this is a particular topic I've always been interested in. TBH, I'm not sure how I feel about Evasion Clause - there's no way that you can say it's broken. Like, at all. Honestly, it's a really bad strategy. DT only gives you a single boost in one turn; compare that to the likes of Swords Dance, Dragon Dance, Quiver Dance (just realized how much time pokemon must spend in battle dancing for crap sake).
Anyway. The point is, there are just SO much more useful things that you could be doing with your turns in battle than relying on a move that has a chancy outcome at best. At this point, I also want to point out that DT/ Minimize users sacrifice REALLY important moves in order to boost their Evasion. The Dragonite thing proved that, but for another Example Set...
Starmie @ Leftovers
Minimize
Recover
Thunderbolt/ Ice Beam/ Toxic
Surf
If you're going to boost Evasion, then you need Recover, for obvious reasons. Add on Minimize, and half your moveset has gone, with only two attacks left to somehow sweep your opponent - and whatever you do, SOMETHING is going to wall you. No matter what. If you don't have Toxic, then special walls (most notably Blissey) are going to wall you till Kingdom Come; however, if you choose toxic, then you're walled by stuff like Jirachi, Tentacruel and Toxicroak to name a few. Then you have the problem of EVs. If you defensively EV, then Surf will be doing pathetic damage, and stuff like specially defensive roost Scizor wall you; whilst if you offensively EV, setting up becomes harder and you're prone to being taken out by a stray, moderately strong attack.
This is just one example; but what it shows is that you don't necessarily even need a counter to Evasion (like never-miss moves, Haze, Perish Song etc) because odds are, something you have on your team will wall the evasion booster. This happens (as shown above) because your movesets become more restricted (as well as problem-EV spreads). Additionally, not everything can use DT to great effect, like many posters seems to be implying. I mean, are you really going to use DT Volcarona, or DT Excadrill? Come on, they have better things to be doing, and just don't have the moveslots (or free turns, no less, for pokemon that are quite frail) to set it up.
Even pokemon that would supposedly be 'broken' with Evasion boosting moves aren't that good (mainly Minimize abusers). Starmie isn't the only example. Take Blissey:
Blissey @ Leftovers
Bold - 252HP/ 252 Def./ 4 Sp. Def
-Minimize
-Softboiled
-Seismic Toss
-Toxic
This, I'll admit, is quite a bit better. However, basically anything that is immune to toxic and can heal off damage completely destroys it. Gliscor, Skarmory, Roost Scizor, Reuniclus, Jirachi and Gengar are all common pokemon that would render this set useless.
So, after that somewhat-lengthy discussion, I find it hard to believe that anyone could call Evasion 'broken' as such. For me, the question is more about whether Evasion is actually desirable in the metagame. It is, after all, a strategy that usually puts the fate of the battle into the hands of the RNG, which doesn't seem like a good thing. On the other hand, if Evasion users are regularly hard-countered by common pokemon, then it seems like the strategy is so bad that, whether the ban is in place or not, it hardly seems to make a difference.
Finally, I just wanted to point out that, even in a metagame with no Evasion Clause, the better player would still win the majority of the time. A skilled player should have some idea of what they would do against the better Evasion abusers (honestly, there aren't as many good ones as people are saying), and have some kind of plan for it. This is on top of the fact that the strategy rarely works. To be fair, though, it does open the possibility of some matches being unfairly decided on by Evasion hax - but if you're talking about outside-chances, then you could be talking about any piece of unfortunate hax in a battle.
tl;dr - I hope I've made something resembling a coherent argument...