Add to the overview that it's slow, please.
Breloom can also use Force Palm over Rock Tomb as a reliable and more powerful secondary STAB attack if it needs to hit harder than it would with Mach Punch, and is useful for getting past defensive threats like Ferrothorn and Mandibuzz.
Rock Tomb does more to Mandibuzz than Force Palm. 252+ Atk Life Orb Technician Breloom Rock Tomb vs. 252 HP / 252+ Def Mandibuzz: 195-231 (45.9 - 54.4%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
Hippowdon can't really easily take care of Dragonite. With Whirlwind it can be an adequate counter, but it's not a great answer, so I wouldn't mention it for that in Team Options. Aegislash and Talonflame mentions stand, though.
On Leech Seed Breloom, I think Spore is definitely better than Rock Tomb. The set doesn't even use Technician or Attack investment, so it's very weak, and it's not like Rock Tomb is doing much to Mandibuzz or Mega Venusaur to justify using it over Spore. I know Pokemon can block Spore, but there's a lot more Pokemon that can be affected by it, and I'd prefer to see Spore as the sole slash.
In Usage Tips, it's best to Leech Seed on predicted switches. Once you've done that, as long as you're not worried about the Pokemon in front of you setting up, feel free to Protect to stall more. Stress that they need to keep Leech Seed on the opponent as much as possible and stall like that. Leech Seed Breloom forces a lot of switches, which is another reason that hazard setters are good teammates.
I requested some fairly large changes to the Leech Seed set, so I'd like for you to post saying that you've done these once you have, at which point I'll stamp. If you disagree with any of the changes, feel free to explain why.