I think it's good for the game. It's a new way of playing. It rewards really aggressive play, but over commit, and you can well be punished for it.
Like everything in this game, it will take some learning from both the Ynnari player and also their opponent.
If you are facing a Ynnari list, maybe it will change how you approach target priority. For the most part, you target units with the express view of wiping them off the face of the planet, whereas against a Soulburst army, maybe a thorough crippling is the best way of playing. Target a flank and dismantle it slowly, so that, if you do trigger a soulburst action, it will be against a seriously understrength part of the force. Any reprisal shooting will be hampered by the fact the unit is already crippled.
Shooting at the Ynnari with weaker units first may make sense. The Ynnari will take damage, but by the time you are destroying units with your best shooters, the army around them is significantly weaker.
Think of playing the Ynnari less as bludgeoning them off the table and more as Death by a Thousand Cuts. Nibble at them until they die. Don't be sucked into taking a big bite.
Can the Ynnari be overwhelmingly powerful? Yes, in the right hands and against a poor opponent, they can.
Can Ynnari be beaten? Yes, by strategising correctly...at least you know that the units won't be shooting then hiding through Battle Focus every turn.