Honestly I don't think quickstrike was meant to really be an attack you just spam over and over as a combo. It's clearly meant to be a movement tool to do stuff like get to the ground before your opponent for example. Removing it's invincibility just confirms that in my mind. Caltrops were and of course still are the better use of your super meter most of the time lol.
Honestly, quickstrike wasn't even very good. So I find the nerfs to be harsh. But, it'll keep it from being like Cowboy's lightning strike, a brainless option you can spam for free. So it's warranted.