Why are Ryude's swords "so good"?

I don't think it's the same boost when you're not capping. Is the 1 extra line better than the 50% boss damage (from weapon and cra set) and 6 attack you lose from a fafnir?

It's the same for all levels of funding. increase = (nAttacks +1) / nAttacks

The only caveat is that if you hit cap without needing the extra %boss and att, this is the only way to increase your damage.