I can understand killing the boss fast might seem like a loss of dramatic tension. I would suggest, instead, using the Tenacity House rule. Taking away the awesome story and narrative that can come from a huge explosion takes away from what OL is about. Making a boss tougher, however, isn’t too difficult. With the current rules you can give a boss Die Hard, Divine Agent, Resistance/Immunity to damage types.
Here is the House Rule that Brain even made for people who were concerned about quick boss deaths like yourself. This isn’t core, but an easy addition: