This is why Desolate Land is banned:[...]
Desolate Land/Primordial Sea: I don’t think this ability is banworthy. It is a permanent 50% boost to Fire/Water moves and Immunity against Water/Fire. It might seem strong when the opponent happens to block your super effective moves with the immunity and retaliate with a boosted STAB, but that does not happen very often. What I’m trying to say is that the ability is pretty situational. Sure, it’s an impactful ability that can also support a teammate on the field, but I don’t think it comes even close to the other banned abilities like Cursed Body and Protean. If this is unbanned, I think we can expect to see a wider variety of sun/rain teams.
[...]
P-DON (Camerupt-Mega) (M) @ Scope Lens
Ability: Desolate Land
Shiny: Yes
EVs: 252 HP / 252 Atk / 252 Def / 252 SpA / 252 SpD
Brave Nature
IVs: 0 Spe
- Metronome
HAUNTS ME (Camerupt-Mega) (F) @ Expert Belt
Ability: Analytic
EVs: 252 HP / 252 Atk / 252 Def / 252 SpA / 252 SpD / 252 Spe
Lonely Nature
- Metronome
Seriously, though. Camerupt-Mega is slow as crap, so it's practically GUARANTEED to get Desolate Land up. And then you can just say bye bye to almost anything that would be super effective against it, creating the world's stupidest tank. If DL and PS were banned, weather-negating abilities like Cloud Nine would be a vital part of the meta.