Wait, Opening Gambit, Damage up and Swim Speed up suck now? I really have fallen out of the meta... Nah damage up always sucked due to the damage cap most weapons have
*shines the Ryechu signal*
Jokes aside, Damage Up is very legit. It's the difference between a charger surviving CQC thanks to half charges getting over the 100 damage point, blaster AoE securing more guaranteed KOs and Octobrush killing in a more consistent 2 strikes or not.
Damage Up also helps a lot of shooter type weapons in terms of consistency of damage output.