Poison Heal is arguably more broken than Guts.
Remember Stallrein? How much does Stalrein heal per turn with Hail + Leftovers?
12.5%.
How much does Poison Heal recover per turn?
12.5%.
Is CAP9 immune to the most prevalent weather effect in OU?
Yes.
Propose to me how we will do anything but create another stall-whore given a moveset like:
CAP9 @ Toxic Orb
~ Substitute
~ Protect
~ Rapid Spin
~ Crunch
Not only will this pokemon perfectly obliterate the opponent's stall, it can actually defeat common counters that only pack one SE move.
Now you could argue you'd just run into another CAP9 eventually and you'd both end up resetting the field. It doesn't really matter, because in such an instance you will remain at full HP and can simply wipe out the next attempt to set up hazards. Point is, it can stall for 32 Turns in a Sandstorm. Woe be unto you if you aren't also packing the anti-stall centralizer CAP9, since chances are they can keep their hazards up if you aren't. If you have your own hazards, you can just wait until Starmie, Celebi and co are in Crunch KO range.
Is Sandstorm the effect in OU with the most pokemon that resist it?
Yes.
Granted, most of these fall to STAB EQ, but what of Skarm, who walls this set to even more ends than the others? What of Bronzong? Something like Metagross could beat the Sub+Protect with Bullet Punch + Other.
Unlike the list of pokemon that are common in OU, that are not killed by hail. The list of common ones is... Zero. Mamoswine is about the most common, and he's not used much.
Stallrein only works, in part, because it's immune to the weather that sustains it. Although this isn't Sandstorm, the fact is, you should have taken T-Tar and Hippowdon out before bringing Stalrein in.
I'd rather wait for 32 turns, then slughter CAP9, by stalling with Skarmory, Hippowdon, ect, ect, than have CAP9 be able to OHKO almost everything in the game with Guts.
Plenty of things beat Sand-Stall CAP9. Few things beat Stallrein, because far more in OU is immune to Sandstorm, and has the bulk to shrug off CAP9's other attacks, while also having the power to either force it to switch out, meaning it has to come in later safely, or force it to stall for 32 turns, doing nothing, or attack, doing nothing important, because of Slack Off/Roost, before being killed, or at least, Whirlwinded away.
Guts is more broken. I've supported that Hail Stall > Sand Stall. If people say guts CAP9 would make Uber, his is kinda like a flowchart for what I just explained.
If Guts = Uber (Under Offensive, it could sweep whole teams without Skarmory/Maybe Bronzong)
And
Sand Stall > Guts
Sand Stall = More Uber
However
Hail Stall > Sand Stall (3 common immunities < 1 rare one)
Therefor,
Stallrein = Uber (Which it isn't, annoying, yes, beatable, yes)