Create new skill without new weapon
Another alternative is to introduce swappable weapon skills for each slot.
Meaning that for #1 you have X number of skills to swap between, same with #2 and so on. But each skill selection is locked to that slot.
Thus allowing variations within a weapon (knockback vs knockdown and so on), but keeping the overall theme of the weapon.
It’s an issue too.
But Anet have to work on it since the game is losing interest.