Rapid Assault no Final Strike property

I really wanted to make a build using spearheads explosion, but the game just won't let me insert the Crescendo support gem



Maybe I'm missing something, but it seems to be pretty clearly written here that it supports Strikes that have a Final Strike, and in the description of Rapid Assault it's pretty clearly written that it has a Final Strike.





By the way, it would be nice if Cresendo weren't limited to just Strike Attacks. For example, then Rolling Slam could be slightly modified for different purposes. With Cresendo, it would be more suited for damaging stunned enemies, while with Stun III, it's more suited for stuns.