I am leaning towards ban on Heat Rock for the following reasons:
- Handling the Sun Abusers for 8 turns(well 6/7) is just to much; as very few Pokemon can take them on and players are generally forced to resort to clever switching to stand a chance. So stalling out those turns is more difficult
imo no one should be trying to stall out 6-7 turns of sun. Stalling anything for that many turns loses way too much momentum. Even if anyone manages to stall out sun turns, all it takes is for the opponent to set up sun again and you'll have to try to stall it again and it's a never ending cycle if that's the only way for you to counter sun teams. If stalling them out is the only way to defeat them, I'd say the team is just not prepared to take on sun teams if anything, but by no means bad. I'd like to think that the metagame has not adapted to weather, and not many even consider about sun teams as threats while teambuilding. Sun teams are pretty much not common enough to be taken into consideration.
There are some problems faced by sun teams though: Trick Room, paralysis, entry harzards, priority and others. Trick Room fares well against fast paced offensive teams generally. Trick Room teams really wreck sun teams from experience it's hard to avoid being swept by them when Trick Room is active. It is hard for them to avoid being swept under sun too though, but most of the time the usual sun inducers would already have taken too much damage or the sweepers themselves did. Spreading paralysis might be hard and might require some prediction. Regirock etc can Thunder Wave Chlorophyll abusers on the switch since it attracts them so much. It's a shaky way but makes revenge killing much more possible. Entry hazards are a boon to Fire-types sweepers, most notably Charizard. Entry hazards aren't too hard to set up in the first few turns of the match when the sun team tries to set up sun. Phazing moves, while rare, helps with dealing sun teams quite well. 2 turns is used to set up sun and switch to a sun abuser. 2 turns to switch to a phazer and shuffle the opponent's team to rack up entry hazard damage. The only bad thing is when you phaze in something that can set up on your phazer. But most of the time whatever that's intended to set up on your phazer would switch in asap and get phazed out. It's still likely to face two Chlorophyll users against a phazing Golem though. Priority is the most common way to revenge kill, especially Absol's Sucker Punch. But a well built sun team can avoid revenge killing to some extent.
tl;dr try to avoid stalling sun turns and prevent the sun abusers from setting up or switching in instead. It's hard but not entirely impossible. I've had times when I couldn't even switch to a sun abuser, let alone set up. The time taken for a sun team to set up is as good as time for you to set up as well, unless you're facing Encore Volbeat, but that's another story.
- It will give us more insight as to whether the weather abusers are broken or if its the longevity of it. I know this isn't a real reason to ban it but it will allow us to know if its the abusers that are broken.
I'd say if a weather abuser is broken in sun, it's still broken without Heat Rock, just that it will be limited to the lesser turns. If it can sweep for 5 turns without a safe counter, it can still sweep for 2 turns safely as well. Though less damage would be done to the opposing team, a broken abuser will still be guaranteed to do permanent damage to the team if it can't be stopped for those 2 turns. Repeat the set up of sun and you can re-attempt the sweep till whatever that's needed. Something that can't be handled in sun still can't be handled without Heat Rock, no matter how many turns lesser. As long as it's too powerful in sun, it won't matter how little turns it stays in the sun as it's still too powerful, even for a short period of time.
Also try taking on +2/+2/+2 Victreebel for 5 turns and tell me Heat Rock isn't broken. Without Heat Rock there wouldn't be nearly as many problems with sun; and even if you do make a mistake and let sun be set the consequences arent nearly as dire. When letting volbeat switch in once costs you the game because of its item I think its to much though many may disagree
It's hard to set up with Victreebel though it isn't entirely possible. I'd agree that a +2 Victreebel is too hard to counter though. Similarly, it's still quite hard for it to set up in order to pull a full sweep. It's so frail that almost anything that isn't completely defensive like Tangela can 2HKO it. Unless someone lets Golem or something like that stay in on Sunny Day Regirock even after sun is up, there isn't much opportunity for it to set up, but I digress. Assuming that Victreebel has Growth up and Chlorophyll activated, there isn't much that can safely counter it. It does suffer from 4 moveslot syndrome though but having to guess what move it doesn't have makes it unrealistic to counter. What are the hard counters to Victreebel without exploiting the 4MS anyway? >.> The easiest way I can think of and tried to set up with Victreebel is to use Volbeat. With Substitute and Sunny Day, it can Baton Pass to Victreebel and often gain a free turn to Growth, which pretty much ends the game.
