are all support gems supposed to work with all skill gems in the end product?

so are all support gems supposed to work with all skill gems in the end product? i was wondering this because before i got into the beta, that is what i thought, and the system really isnt as good as it should be if it's going to stay the way it is now.

im not saying all of them have to be viable modifications to skills, but they should atleast work. for example, arrow rain and multiple projectile together doesnt do anything right now. considering arrow rain is a projectile, why does it not work? i was expecting it to either so there's more "pulses" of arrow rain on top of each other(although this is probably too good to be true) of just 3 seperate arrow rains, one where you aimed and others around the area.

that's just one example, there's countless supports and skills that dont work together right now, so here's the question again: are all support gems supposed to work with all skill gems in the end product?

No, some combinations wouldn't make sense.

Also Rain of Arrows isn't actually a projectile skill, it's just able to benefit from projectile effects for consistency with the type of builds that would use it.

What you want seems more reminiscent of a doublecast or multistrike support, which don't currently exist.