This happens so infrequently, its not even an issue worth addressing. This is almost as sad as the Sastasha (or other ARR dungeon) drama that invades my Novice network feed every other week.

Fact is, if the boss is at 20% HP or lower, and I know that I can solo the boss, and my party has been collecting vuln stacks or otherwise playing extremely poorly, I'm going to solo it whether the party likes it or not. Call it a learning experience, blame whatever you like for it.

This issue can often be easily resolved through the power of communicating with your light party in an adult way.