Daka and RG are basically essential already, and this does nothing to nerf Dooku since they're simply taking away a slight amount of dodge and then giving it right back to him by not allowing opposing players to dodge his stuns. I already see nothing but Dooku/Old Ben, Daka, RG, QGJ, Rey builds in arena, and I don't see anything about this update that will change that. Maybe Old Ben is now brought down to Dooku's level a bit, but otherwise not much to see here.
What WILL happen is people will see way more stuns in arena, making tenacity builds a lot more important. Characters like Yoda, Luke, and Magma will all benefit from this change, albeit only to the extent that people use more stuns, which they already seem to do quite a bit.