well kaido and big mom are kinda stupid.
but given that more than 90% of one piece population are fodder i can see the appeal to amass such types of weaponry.
the beast pirates have cannons that can one shot ships.
wano produces weapons for the outside world, and doflamingo was selling them in the black market.
germa...pacifesta...ceasar clown chemical weapons...
yamato's ice wall is more durable than big mom
anyone who can use haki properly can survive explosions.
kinemon cut a massive point blank explosion back at punk hazard.
kaido's dragon breath can obliterate mountains in a split second, but most powerful people can tank it just fine.