Fives without Omega mat for his basic attack is not OP and can be dealt with pretty easily.
I think it is kind of unfair to compare Fives with a lvl8 basic with other toons not at the same level. How does it compare with Daka and her +15% stun? What about GS and a +15% damage
I'm pretty sure some of the other lvl8 abilities we will find are equally powerful and will negate the devastating effect of Fives' counter + double tap.
Just a thought...