Build up photon arts

Can someone please explain why some build up photon art require multiple charges to use? Why does the cannon (which is arguably the most powerful) only need 1 build up charge but the sword requires 3 charges to use once? This seems kinda backwards to me.

It might be based on how frequently the weapon is used, the launcher is a secondary weapon for me as a Ranger, and I go for the rifle most of the time. I end up using the Build Up PA mainly on bosses to take them down faster and sometimes I need 3 attacks on the same boss or to drop two smaller bosses quickly with single attacks each.

I think having the larger build up on a primary weapon makes it so you can't spam a very powerful attack, making it so you still need to learn other class abilities. By default it takes doing a lot of damage to even get one charge on a Build Up PA ready.