He will always be viable, he is still one of the stongest toons in the game. The only question is: is he viable enough? When they began to break the game with OP toons and Hero's journey toons they undertook something which has no turning back. They can't nerf every toon at the same time, they will just continue releasing ridiculously strong toons to break the meta they previously created.
Uh, we broke the game with CLS, what are we gonna do? Imagine the scenario of that meme where the guy saying the clever thing gets thrown out of the window: release more CLSs but stronger! Rework toons to make them ridiculously OP! Simply nerf cls and go on releasing normal toons so the game is balanced and the better strategy wins!
...
*gets thrown out of the window.
They released CLS and they broke the game. So they released Rey and they broke it further in addition to breaking cls too. When every single player from 20 to 1 in every arena had the same team, hey! I have a perfect idea! Let's take Palp and Vader and let's make them ridiculously strong! So we won't have to work on another OP char and we can sell other OP toons as a remedy to this meta. And here we are. The current meta. We just have to wait until they release something which is even stronger than Palp+Vader+ZSion.