Kind of suprised to not see Athar not up there, maybe their benefits like henchmen and quest maps are not great for AIs...
I don't know how much the AI changed since 983, but my game ended with a big knock-down drag-out between me (Lady Porcupine, apparently) and Relias. Relias had been doing very well and conquered Yithril, Gilden, much of Tarth and Magnar (before they surrendered), and so out-powered me about 450 to 150 (or maybe more, don't remember exactly). I think the AI leveraged henchmen quite well as long as it was winning: they kept leveling and got better equipment, etc. Once I pulled off several major tactical victories (through extensive magic use) they seriously underperformed without good enough supporting troops, but I'm not sure he ever stopped building them. By the time my armies caught up to his they were a liability, either by having too many wounds to be useful and taking up army slots, or by being outright negative with dysentery or whatever that wound is that gives -x% to army hp. In fact, when I started rolling up his cities he lost any chance he had as all his henchmen would respawn in cities but be immobilized, and then when I attacked his troops were at a total -50% hp thanks to multiple cases of cholera (or whatever). (Not to mention Relias had a base hp of 3 thanks to the useless familiars he kept summoning, but I take it that has been fixed.)
[Re: Quest Maps: does the AI even do quests?]
Quick fix: don't let malaria (or whatever it is) stack.
AI fix: teach the AI when a hero or henchman becomes a liability and have it put him/her out to pasture.
Mechanics fix: have heroes (or at least henchmen) die for good at some point. Alternatively, perhaps tone down wounds a bit (and/or put in a healing mechanism) but cause the hero to drop an inventory item upon defeat. (So the setback is serious but temporary.)
Aside: I think "sidekick" is a better term than "henchman" because henchman implies a faceless goon whereas sidekicks traditionally have some personality, but less of one than a hero.