My idea for activated weapons is to have the special a toggle activation, and its use uses stamina instead of having a cooldown or set number of swings. This is aside from psyker’s force swords, because they already have a resource system tied to their use.
This eliminates the need to have to constantly reactivate them, which is an annoyance, but also balances them innately per class. Using stamina for greater damage and stagger output makes balance sense because stamina is a defensive resource, so you’re actively (pun intended) choosing to sacrifice defense for offense on demand (of which the concept already exists in a vet talent, though is always on instead of activated in that case):
For vet, which has lower stamina and regen, won’t get many uses from a power sword, and will take some time to regen their stamina for more uses, so they can’t go constantly ham on a horde, but can use it effectively in controlled situations. It could also make chainsword more appealing (that weapon needs some buffs anyways). If they want to have more uses for the sword, they can take a stamina curio, which sacrifices toughness or health, so it’s a balanced tradeoff for more power. Power cycler, for instance, can instead refund half stamina used if an elite or special is hit.
For zealot, which has higher stamina and regen by nature, can make better use of chain and power weapons, which makes sense considering they’re supposed to be more melee oriented. Same consideration towards more stamina/regen on curios to keep up powered hits in extended horde scenarios.
Ogryns will meet somewhere in the middle.
I think this simple change would solve both the issue of the annoyance of having to constantly reactivate weapon specials, at the same time limiting their use in a balanced way that makes sense per character.