Boss Fights really depend on how accessible you make them.
If your not Fully informed (as the GM) about the Bosses abilities, and Let an Intelligence Boss stand and slug it out when he is outnumbered, then you may be doing it wrong.
Note I am not saying your doing it wrong, I am just saying that I encounter a lot of Gms, New and Old, in rolemaster, that don't Fully utilize the abilities of their Npcs, monsters, and Bosses.
For instance, I Always Make sure My Melee Npcs and Bosses have Disarm Foe. And I have them USE it.
If the Boss is going to be outnumbered, I have him Maneuver to a More defensible Position, where The PCs can only get to him 1 or 2 at a time.
( I apply penalties for firing missiles or spells into or through a Melee)
Spells can Be the Biggest Thing overlooked. What Magic does the Boss have access to, did He have time to prepare? Does have have Magic items for defense or offense, Defenses should always get activated first. Does he have the ability to Store spells for instance activation?
This is the biggest a about magic that I see overlooked when converting a Module to another system, especially Rolemaster.
D&D/Pathfinder Spell system is completely different than Rolemaster.
When I convert (I am currently working my group through a Modified Desert of Desolation from OAD&D conversion) I make sure to account for the differences in the system and "Upgrade" My bosses abilities to be Rolemaster appropriate.
I especially Pay attention to defensive abilities, since these are More important in Rolemaster than any other system I have gamed or GM'd in.
I also look at whether or not it makes sense that a Boss would be Fought alone.
This can Make sense in Slug-fest style game systems like D&D, where it is mainly a matter of Depleting Hit points with no other real ability to defeat the foe.
For instance, I have an Illusionist opponent in my current Game. He already has a constant defense in that he has a Visual/feel/Sound Phantasm always up duplicating his own image, with an invisibility spell cast on himself. Anytime he interacts, even with his own henchmen, it is through the Illusion of himself.
If he feels the situation is going bad, he will set the phantasm up t meet and react with the Enemy for a Few rounds while he is invisibly leaving through the escape route.
If it is on the NPCs home ground? and they feel they out numbered? They are not going to just Stand and fight/slug it out with the PCs. They are going to run to other areas to gather forces and/or better terrain to for them to fight in, use choke points to limit Pc access.
One thing I always Hate/Hated about many Modules, old and new, and the way the GMs ran them, was that they read and are run by many like Video games with Basic Fight to the death AI's
Take your game to the next level and run it Real.