91647517792:DoTs are quite strong if they aren't being countered
Many DOT effects do very little damage more than single-hit abilities when totalled up. Usually the only benefit is higher accuracy and the POTENTIAL to be combo'd with other effects... many such effects (Mangle, that trash Black Claw, Exposed Wounds) do no damage themselves for that turn. So you may see "OMG DOT + BLACK CLAW OP PLZ NERF" but it's really just 2 turns' worth of damage that took 2 turns to set up, and offers many opportunities to swap.
1 move, Sandstorm, should not kill half the metagame just by potentially being present. It's no different than when Fluxfire was doing its thing. Sure, I capitalized and rode my Oily Slimeling to many free wins... but having to always design my team around "How do I not auto-lost to Fluxfire" was not a fun aspect of the metagame.
Even at half the reduction, Sandstorm would prove to be a massive hindrance to DOTs/multi-hits without outright killing their presence in the metagame. If DOTs are a big concern, the Aquatic racial buff as well as Cleansing Waters should be right up your alley. And there are a handful of pets with shell shield style effects. Your argument on DOTs implies you have no options to address them without Sandstorm at its current absurd power level, which just isn't the case.
The point of a diverse metagame is that you can't just select 3 specific pets to shut down every enemy strategy and auto-win.
Right now, since 5.3, my win-loss ratio with the team I've been PVPing with is approximately 35 to 2, and 1 of those losses was on the heals of 2 25% stun successes against me, 4+ misses at 85%+ hit chance, and 0 enemy misses at 70% hit chance... which went down to the last turn where my immortal undead killed the enemy pet before the round ended, and the game randomly gave my opponent the "win" despite being KOd first. All in all, I've had exactly 1 legitimate loss since 5.3. I'm not playing any of the metagame junk, no Sandstorm, no Raptor DOT team, no Darkness, no Kun-Lai Runts, no Win-By-Graphics-Lag Lightning-Cyclone abuse, none of that. (To be honest, it's mostly Direhorn Runt doing the heavy lifting but my other 2 choices do a good job combating things that do well against said Direhorn, as well as acting as checks to specific metagame threats.)
EDIT: And, in fact, Direhorn Runt may be overpowered. Primal Cry combined with a moderate speed and Horn Attack shuts down a lot. Even if Critters became CC immune, they'd just flat-out die to Beast damage. Maybe Primal Cry is overpowered, maybe Horn Attack is, the combination of the two (which I USE mind you) is probably overpowered. I've also made Sandstorm abuse teams with the current poor selection of users, said teams went undefeated and were long drawn-out unfun matches. I do test these things before making a big fuss about them.
Anyone can have an awesome win-loss ratio by understanding the metagame and building around it. The problem is going to come when Sandstorm just becomes the only metagame and players aren't allowed to competitively use Frogs or Oozes or most Critters or most Undead/Fliers, etc. Right now, I face a LOT of variety and have struggled more with some of the wackier things like Thundertail Flapper than Kun-Lai Runt. I don't really want the Fluxfire-style metagame back where I have to run a specific anti-Sandstorm team. I got REAL tired of having to run Oily Slimeling, Nether Faerie Dragon, Scourged Whelpling/Infected Squirrel or just lose because I couldn't account for the abundance of Fluxfires and Fel Flames (most peoples' anti-Fluxfire choice).