Like any kit in this game, you need to recognize the opportunities to be aggressive, and when not to be. The Slayer walks a fine line.
If you really are as aggressive as you claim i don't understand how you could think the Piranha is a downgrade to anything. At point blank range there are few weapons in the game which compete with that (there's a reason GI / Piranha is an ultimate boss killer .. yes I know, increased accuracy) The only slight drawback is the increased CDs. However at the range a Slayer is at you can easily land all pellets anyways, just not all of them will land on the head.
When I play a Slayer, the only time i'm not right in the enemies grill is when there's a hack or escort. Who cares if I'm not killing stuff while that happens, those enemies will respawn anyways
GI not only has increased accuracy, but increased accuracy, ROF, 80% damage from cloak and a freaking 20% damage buff from the Proxy mine. It's not even in the same league.
Plus if you do U/U, you will have to choose between Incendiary and Disruptor ammo. Talon has 150% damage bonus vs shields/barriers and Piranha doesn't. So it'll take forever to take out either Atlases or Praetorians with it. If you have Disruptor ammo - Armor takes along time to kill, if you have Incendiary - shields/barriers take a lot longer to take down than with Talon/Hurricane.
As for RC, you need to think about it and pull it off consistently. So if you get staggered or press to early/too late you eff up your reload and have to try again. With the other 2 the reload is nearly instant and frees up your brain capacity to think/observe other things instead of getting frustrated while getting staggered by Scions/Primes.
Talon/Hurricane is much easier. That's just a plain fact.