In the remix cup I sac swapped jeli for a sunny castform and they solar beamed me :( I did not know he could solar beam
Energy Ball is 5 more energy for the same damage…that’s barely one more fastmove…the difference is really pretty small between them. Doesn’t really justify spending an unholy amount of TMs for a marginally better move. Yes, the debuff chance isn’t very high but getting it can be really nice, especially when a lotta open UL 'mon have such high bulk.
One more fast move is two turns (with SC) plus you cannot stack up two of them. But of course, it’s not another league or so. This is why I said, if you’re looking exclusively for a grass charged move and you get energy ball, ok. If you’re just up for any good move, I would probably continue rolling the dice.
In this case, Grass coverage is I think better. Most Swampy don’t shield Mew thinking it’ll be Flame or Wild Charge or at best Dark Pulse.
Which team? With steely stuff, for sure you’ll need the swampert coverage. Otherwise maybe not. E.g. a tanky core with umbreon and GirA or poliwrath covers swampert alone pretty ok.