Depending on how you define viable. Tesla has just shy of 800 SC that are in operation. Electrify America has just hit 400 locations in the US. I think that's pretty viable if I were driving a non-Tesla EV that had level 3 charging capabilities. That's not even factoring in all the level 3 and 2 ones out there, networked or not.
I do think Tesla SCs give the best user experience. Most, if not all, of the other ones would require activating the charger via app or credit card, which isn't as seamless, but it does charge up the cars.