I just answer coltraz question the function of double counterslash on zephyramus. But I get your point its basically abuse. its even more powerful then infernicorn.
Thunderseal and dream ender need 3 low star to ohko myth (no crit). (4,6k -5k damage)
Double Counterslash only need 2 low star to ohko myth (no crit).
And “maybe” he only need 1 low star to deal damage like bundam with Void powerslash.
Actually I don’t have this monster ,just from experience meet the user. But I am sure double counterslash only need 2 low star to deal that damage. 
Low star= (SE or lower)