Your solution isn’t a solution.
Your solution is a symptom of a bigger problem.
The problem is not that any given boss is too loving since the odds of getting up from a boss with no adds is about zero if you go down in the first place. The problem is that “damage output” really is the summation of the game. You can almost read the coefficient of a skill and know whether it is worthwhile or not since longer fights with fewer enemies increase danger levels exponentially.
You want more skilled gameplay? You don’t change the stats of the players, don’t demand more dodges and don’t reduce rally mechanics; if you want more skilled gameplay you need to make the opposite rules true:
Battles need to be more “Wars of Attrition” where surviving them is actually a matter of withstanding inevitable strikes rather than racing to deal incredible amounts of damage and enemies should actually hit less hard but hit more frequently reducing emphasis on perfect active defense (blocks, evades) and focusing more on granting passive defense (toughness, healing power/regens) a more active role in survival.
Your solutions would actually only have the opposite effects of your intentions. And for the record your “suggestions” are actually already in the game. That was what HoT was on release basically. And every-casual-one hated it.