vale snow
The goal of it was to streamline Grimden and make it easier to understand that you get a bonus on [Mortal Arts] specifically and I get the sentiment and appreciate how creative you can get, but it wasn't certainly meant to become God while nuking the boss at the same time.
Simply diminish the bonus that will be applied to the next instance of Enhanced Mortal Arts with a Focus Loss for each offensive action taken prior to it capped to an iconic 5 (excluding Phantom Strider's dash 
. It does 0 damage, but it might be considered an offensive action if I know this game well).
I.E: using Decimation, Spine Snap or Agile Strike will reduce the bonus applied to Mortal Arts
torpid dock