I think the considerable thing about Rillaboom is that Grassy Terrain is very much a double-edged Sword, but you really have to play to it to make the mon put in work. A decent couple mons definitely lose some teeth with Earthquake's power cut (Physical Lando, Dragonite into Steels, Iron Treads, Roaring Moon), as well as some defensive mons becoming EXTREMELY passive (or even more Passive) like Gliscor and Ting-Lu, which can open set-up/Revenge chances for things like Bulky Ghold, Booster Crown, or Raging Bolt.
At the same time, the Terrain can benefit opposing exploiters I mentioned if you throw Rillaboom around, as well as both sides standing to gain from things like Ogerpon-W or passive healing on bulky non-healers like Tusk, Zama, and Gambit.
I think Rilla's big issue there is that it's not bad, but the Terrain does A LOT more to consider in the Meta compared to something like Psyspam not having to worry about Psychic Terrain's effects enemy side or Past Gen Misty Terrain on Fini just being something you could account for in the teambuilding stage (i.e. don't depend on Status or load up on Dragon Attackers). While there were debates about a Theorymon Gen 9 Tapu Koko before, I could see Electric Terrain having the same issue, and we even see a bit of it with Sun teams having to deal with potentially boosting an Enemy Tusk or Bolt. Rillaboom genuinely requires you to build the team around it because Grassy Terrain is a factor that will typically outlast the Pokemon, positively or negatively.
At the same time, the Terrain can benefit opposing exploiters I mentioned if you throw Rillaboom around, as well as both sides standing to gain from things like Ogerpon-W or passive healing on bulky non-healers like Tusk, Zama, and Gambit.
I think Rilla's big issue there is that it's not bad, but the Terrain does A LOT more to consider in the Meta compared to something like Psyspam not having to worry about Psychic Terrain's effects enemy side or Past Gen Misty Terrain on Fini just being something you could account for in the teambuilding stage (i.e. don't depend on Status or load up on Dragon Attackers). While there were debates about a Theorymon Gen 9 Tapu Koko before, I could see Electric Terrain having the same issue, and we even see a bit of it with Sun teams having to deal with potentially boosting an Enemy Tusk or Bolt. Rillaboom genuinely requires you to build the team around it because Grassy Terrain is a factor that will typically outlast the Pokemon, positively or negatively.