Well, at least they lower the event heroes bonus stats and Ronan isn't too significant for this event.
Remember the pain when you didn't get Seraphina, dat 400% stats boost lol
Yes the 150% stats won't make much different, although it will help in the event if you have full spec equipment on him, he might be able to get more cones for you.
As far as I see, ninja refresh is pretty much the key element in this game. Keep refreshing to clear a round, but the enemy attack first will kill you in their critical no matter if u using Ronan or not.