Combo's E is one of the more easily cancellable abilities there is. You can get countered by your own target or anybody else by just attacking you or they could get flung from someone else where you can't hit them. This is bad since combo's combos require the user to remember each combo and pick the direction they want the enemy to be flung, which most combos require. All this in the time it takes for a punch or a third party to shoot a projectile, while you do three inputs from memory and pick a direction.
So after listening to rant, I present to you: Only the target can attack you, all other projectiles phase through. The target and you will get free movement, you will get 10 percent faster movement during duration, the target can't use abilities but can counter you using punch. Duration will also increase 1 second per each move hit (including normal punch) and there is a visible visual indicator for when combo starts.