Had a thought; maybe it’s not a bad one, let me know.
Cassidy should have something like Ashe’s dynamite toss instead of the grenade as it is. It fits with the cinematic he was in with Ashe & Echo, and is already known to be a pretty fair combo, at least I think so lol.
Then, going back to the cinematic, Ashe can double-down on the summoner vibe her ultimate gives her. So she can get two abilities in one, to replace the stolen ability.
Still with me? Ok let’s go.
It can work like Moira’s orb; you hit E & get prompted to either left or right-click. Picking left summons an omnic, for a few seconds & less than Bob, who is easier to take out than Bob. Right does the same, but summons an omnic that does something different. Both should probably focus on utility more than damage, but they should also do some damage.
Maybe left (calls a omnic that) does something like Sojourn’s orb & does minimal damage but increases your vulnerability; giving her the space-taking part of her dynamite.
Then, right-click can be a lock-on, like Lifeweaver’s heals or Zen’s orbs, that calls a delayed assassin omnic. The assassin applies anti-heal for 0.5 sec, 0.628 sec after you cast it; and deals 40 damage 1.118 sec after cast. Alternatively, the assassin bot can apply a damage over time effect that deals heavy damage without the anti-heal; making it the burning effect from her trick-shot.
TLDR:
Give Cassidy Ashe’s dynamite combo; giving him an ability that fits within the lore of his character & is already in the game.
Give Ashe some omnic summons to replace the dynamite; changing from a fairly mechanical & high-skill floor hero, to an “easy to learn, hard to master” & game-sense oriented kind of hero, which also fits within her lore.
If you’ve made it this far, thank you 
PS: if you see what you like, I can totally take payment for further consultations. 