It might be too late to sway any opinions, but as a UU player, I thought I’d share my thoughts.
I usually play one of two UU teams: A balanced team (that features Breloom) and a stall team (that does not).
I, in my experience using and countering Breloom, do not consider it nearly as scary as many of you. This is what I have found.
It seems the biggest issue is that people dislike Spore. Fair enough, it can be annoying, but I feel people forget all the ways to avoid it: Switch to a Grass type, switch to a Poison Healer, switch to an already-statused mon (extra points for a Flame Orb user), or use something with Natural Cure that can easily cure itself.
You argue that you spend the rest of the battle 6vs5, but why haven’t you considered a Heal Bell user? That’s not something that is used just to counter Breloom - if you’re so vulnerable to status, it also heals every other condition and can save you from multiple threats.
One of the best ways to deal with Spore is to allow Breloom to Spore a wall, switch in to a counter (preferably one that cannot be Pursuit-trapped), and scare him out. Breloom is rather frail, especially without Spore at his hands (since your slumbering wall will trigger the sleep clause if he tries), and usually succumbs to even a neutral 2HKO. If your wall is reliant, he’ll be able to take a hit or two while sleeping, wake up, recover (if he’s a good wall), and bam! Breloom accomplishes little to nothing.
You also speak as if every Breloom counter is sub-par, but I highly disagree. Let me name some:
Gengar is faster, immune to Mach Punch, resistant to Bullet Seed, and has super-effective STAB. (The downside is the Pursuit-vulnerability.)
Mega-Manectric takes about 1/4 damage from Mach Punch, and PUNISHES with Overheat. Furthermore, its Electric type moves scare Mega-Aerodactyl, which is a common teammate.
Latias is already a great mon, is resistant to both of Breloom’s STABs, and has super-effective Psychic to KO him with. She also has a variety of coverage in her movepool that can be used to counter other threats, making her a great multi-tasker and Sp. Attacker. The downside is the vulnerability to Pursuit.
Togekiss is usually faster - especially using the popular Choice Scarf set - is doubly resistant to Mach Punch, resists Bullet Seed, MURDERS with Air Slash, and resists Pursuit. It is a great mon to use regardless of whether Breloom is on the opposing team, and a fantastic Breloom counter - you need to watch for Rock Tomb, but I haven’t found that to be a huge threat in much experience using her.
Chandelure is immune to Mach Punch, resists Bullet Seed, but needs to watch out for Rock Tomb. It has access to Energy Ball to surprise water-types that switch into it, which is cool. However, Pursuit is a big threat.
Mega-Altaria is nice to use in general thanks to Heal Bell and makes a surprisingly good wall - I personally use her on my stall team. Her basic form has a double resistance to Bullet Seed and a resistance to Mach Punch, her Mega form is no longer weak to Rock Tomb while still resisting the former moves as well. Also, Hyper Voice demolishes Loom’s SubPunch strategy, and has reliable recovery with Roost. Not to mention, if basic-Altaria gets spored on the switch in, she can easily heal herself with Natural Cure.
Celebi is immune to Spore, resistant to both Loom’s STABs, and takes neutral damage from Rock Tomb. Psychic can OHKO our poor mushroom-cap, and it’s able to Leech Seed whatever Loom switches to for recovery and annoyance. It needs to watch for Pursuit, though.
Decidueye is a less common counter to Breloom. It is immune to Mach Punch, resists Bullet Seed and Rock Tomb, and is a trapper (which is always cool). It can recover with Roost and has access to U-Turn, which is helpful in switching while negating Pursuit’s extra damage. Oh, and Spore has no effect on it, too.
Volcanion takes only neutral damage from Bullet Seed, is faster, and able to hurt it with Fire Blast or Sludge Wave. It is also somewhat bulky and can survive a hit or two, and is a great Pokémon regardless of whether Breloom is involved.
Gliscor is a fantastic defensive Pokémon. Poison Heal makes it immune to Spore, it takes neutral damage from Bullet Seed and resists Mach Punch, it has access to Recovery, can cripple with Toxic, and is able to stall as much as it wants. It’s usually faster than Loom too, and Ice Fang makes getting rid of the mushroom pretty easy.
Heracross takes neutral damage to Breloom’s typical move set, and usually uses Guts + Flame Orb, making it a great switch in to Spore. It is faster than Mr Mushroom, and can OHKO with its Guts-enhances Attack, making it a pretty awesome counter. It also resists Pursuit.
Crobat is incredibly fast, resistant to both Loom’s STABs, but has to watch out for Rock Tomb. However, it is very easy for it to KO Breloom with the latter’s 4x weakness to Brave Bird. It’s a great switch in to replace a Spore-lure.
Doublade, while slower than Breloom, is immune to Mach Punch, resistant to Bullet Seed, and is bulky enough not to be scared off. However, pursuit is an issue. (Thx MewBby)
Anything else with a Fire/Flying/Poison/Fairy/Psychic/Ice move. Breloom is pretty frail and is easily 2HKO’d by even a basic coverage move. Even switching him in can be difficult, because it is so devastatingly weak to so, so much.
I, personally, like having Breloom in the metagame. I think he’s fun to use, but as someone who uses Togekiss and M-Altaria, I’ve never had any trouble against him.
He’s one of UU’s treasures in that he makes the game interesting - he has a niche, he makes you think out of the box, but so do many other Pokémon! And isn’t that what makes the game interesting in the first place?
Breloom only becomes dangerous if you let him boost.
.......But doesn’t that go for every offensive mon?
Don’t forget that he’s painfully slow; anyone who is faster and resistant to Mach Punch should have no problem dealing with this little guy - and remember that UU is very Fighting-resistant.
I really hope you vote not to ban this little guy. He’s powerful if used well, but he’s weak if countered well. In the end, he’s no scarier than Scizor is - and at least Scizor has a bit of bulk to him.
Good luck everyone. ^^