yeah, writters are problematic, because they often like their own characters too much.
sure, boss characters deserve to be cool, cooler than the PCs even, but not so cool that the PCs can only stand and watch and have no chance to do any cool stuff themselves.
a general advice, I avoid stuff like that with numbers.
if all you have going is a single super bad dude, you need to enormously boost that thing up so it can deal with 10+ PCs at once.
instead, make that one dude weaker, but give him a good handful of non-grunt henchmen, each of them strong enough to make a difference. varied abilities and combat styles on the grunts, different resistances, different weaknesses, so the players spend a bit of time on figuring out which enemies they can take on well, and which resist their stuff. when there is 6-7 enemies, it doesn't matter if one of them is entirely immune to one of the players abilities. A nasty suprise, but that doesnt render the char useless.
That way, the super big bad also doesn't need a metric ton of various actions, it's all neatly split up, giving the PCs enough opposition to threathen them without seeming overpowered.
once the fight gets really difficult, give the enemies a bit of knowledge about what to expect. nothing stops them from coordinating themselves, so 6-7 small actions suddenly turn into a combination of fuck-you that suddenly knocks the most dangerous PC out of commission, and in the end, encourages the PCs to do the same. Right now, everyone is just blasting stuff at their own leasure, a team only in name. Once they start synergizing, actual play begins.
right now, all the RP is just outside of combat, with character dynamics all over. Once combat starts, everyone is on their own. Why not have the various shipping pairs work out dual-tactics, combine their attacks, focus their efforts, protect eachothers back. suddenly a fight that is mostly number crunch can actually become a scene with character interaction