I've no strong opinion on puzzle battles other than they don't offer much replayability. They can be interesting to figure out, but after you know the solution, the fight becomes busywork on subsequent playthroughs. After understanding Grym's gimmick, the only things you have to fight are the inconsistent damage zones on lava. Not a great fit for a game people will want to replay to explore different story outcomes.
Grym is a product of the rule of cool overriding good sense in the end. Someone on the design team thought, "it would be cool if the players fought an ancient golem in the forge". Of course, an ancient golem would turn a party of 4-5 level characters into fine paste. So instead of listening to good sense and saving the golem for later, it was given an easily exploitable weakness. I don't know how we can go from this to fighting cutpurses or Flaming Fist members on the streets of Baldur's Gate, but at least we got a cool setpiece fight.
