I think there's a lot of things that make Froslass's spiking unique. The Speed is a huge, seemingly underrated one - it's that stat that ensures she gets two layers against basically everything with a Sash, after all. The ghost type, too, is huge because of the thing with the spinners. I think Omastar is greatly undervalued (and I'm really happy to see so many teams resorting to it with Froslass still in the game) since it is a much better Pokemon at contributing to your team beyond getting Spikes up (well, being a spin blocker vs. being able to do slightly better damage and being able to take physical hits and counter a few Pokemon, anyway).
As someone who plays about half my games with Rain, I definitely prefer enemy Omastar to be running Swift Swim. It's been mentioned, but all my sweepers are going to outrun a defensive Omastar anyway, and more importantly, I'd say about half of Rain teams lead Uxie. It gets to U-turn after the Surf and bring a sweeper in for free if you have Swift Swim. I think we can all agree Shell Armor is (duh) the better trait if you aren't running rain yourself, and since it's better for rain if you have it... why would you ever run it? The only thing it really helps against is secondary rain set-up mons - though one potential option for that in Electrode outruns you anyway, and some others like Registeel are slower regardless.
I can't speak for Deep Thought's Smogon Tour journey, and I was gone during the UU tour during week 3 (thought I think it was telling that there was no rain whining about/during the tour in this thread or the rain thread, since I DID read them from my Blackberry on a boat ride one day), but I do feel like I can speak pretty intelligently about my own path today, at least. And I really should, since you've indirectly mentioned me.
I had two matches where I ended up down to my last Pokemon with some luck involved both ways in each. I had at least four matches that were determined by one side or the other making a handful of better predictions than the other (win vs. HR, loss vs. AM were where it was most noticeable). There were no matches I won by more than 3-0 (except for the exhibition for 2nd, which was rain vs. rain with Deep Thought, anyway). Two opponents had Toxicroaks, both made decisions with them they'd probably not do again if given the opportunity. I had pretty decent luck (I don't feel it changed the results of any matches, but it was definitely on my side throughout the night) in several matches. I also know for a fact that there were at least six other users using Rain, none of which made it far enough to be noteworthy.
It's worth noting that I fought AM a couple days ago on the ladder and did significantly better with my non rain team (I think he had one mon left with 50%ish, whereas today's match I believe was 0-3, though it was largely determined by him making better predictions against my Ludicolo than I made with it). He went as far to say he thought I would have been better off with my normal team (though I suppose users aware of the history know better than to put too much stock into what either of us said to the other, I guess).
What I'm saying is that I didn't play any matches where OMGRAIN steamrolled through my opposition. All the matches were close, there were decent bits of time in most of them where I didn't have control, and in every match I had today (including and especially in my loss), the team that made the better predictions won. I don't think any of my opponents would tell you they lost to me because I happened to be using rain (except maybe HR, apparently. lol).
It's a strategy like any other, I won when I played better than my opponent and lost when I played worse. I would agree it's powerful enough you Damp Rock being a suspect wouldn't be completely unreasonable, but what is unreasonable is the whining a lot of supposedly competent players do about it.
