Well, everyone knows normal weapons are inferior to specialized damage weapons due to the fact that you can simply wield two weapons with different damage types and deal extra damage to four monster families, while being neutral to the other two. In order to compensate for normal damage weapons' weakness, I suggest that there be a universal buff to ALL normal damage weapons which will increase their damage by a fifth. In fact, OOO did do this a while ago to bombs and guns (blitz needle never needed it, but whatever).
So this will include...
Swords: Triglav, Sudaruska, Dread Venom Striker, Wild Hunting Blade, Cold Iron Vanquisher, Leviathan Blade, Lionheart Honor Blade, Scissor Blades & Winmillion.
Handguns: Iron Slug, Supernova, Neutralizer, Volcanic Pepperbox & Valiance.
Bombs: Deadly Shard Bomb, Irontech Destroyer, Big Angry Bomb & Nitronome.
I only included the 5* weapons (and Winmillion) because those are the ones that count in the end.
TL;DR: 1/5 damage buff to ALL normal damage dealing weapons.
Edit: Changed it to 20% damage increase and included Neutralizer
Each weapon is different. Calibur charges can be strong enough. Troikas are just slow. Iron Slug is extra weak (compare damage to neutrals on callahan) AND lacks a status. Pepperbox is weak but has fire compared to blitz.
They all need a buff, but global tweaks aren't helpfull. Also 1/3 can be a lot. The difference isnt so big to justify it. I'd chose 1/5 at most.