Ludicolo can easily be revenge killed by 100 base speed Pokémon with Choice Scarf. Honestly, I never found Ludicolo to be broken in rain. Blissey still walls it and its defenses aren't anything special without investment.
The only truly terrifying Swift Swimmer in my opinion is Kingdra who can outspeed anything in rain and has no weaknesses except Dragon.
The only truly terrifying Swift Swimmer in my opinion is Kingdra who can outspeed anything in rain and has no weaknesses except Dragon.