Both of the games that I've done extensive exploration of the nodes on Myrror I've found a Sorcerery node with these guardians. This is the hardest combat that I've encountered in the game. (There was one sorcerer's fortress that was guarded with four spellcasting heroes that was a serious problem, but it didn't have anything like this raw power.)
My go-to solution to hard battles is a nine elite paladin brigade. This is no solution to a situation like this. Those paladins are on a suicide mission. They can't take all those flyers.
Several people on the forum love halfling slingers. They stipulate admantine weapons which necessitates that they were produced by a city on Myrror, and give a list of spells as long as your arm. This makes you think that investing that kind of power in any unit might very well do the job. If I cast flight, true seeing, invulnerability, and maybe a few other spells (i.e. lionheart, holy armor, holy weapons, maybe berserk or regeneration) on each and every one of those paladins who in this scenario have adamantine weapons, they might very well be able to pull it off. But I don't consider this a practical solution.
High-level, itemed up, and spell-buffed heroes might be able to take this encounter. So far, I haven't produced the team that I'm sure could. The real problem is that heroes, especially after you've done all that work on them, aren't expendable. I hate to put them in situations like this because it would be real easy to die in that node.
The real reason I'm writing this is to give a big hat's off to the guy whose forum post I read who made a simple, practical solution. Produce nine flying warships. It would be better to cast Flight on each of them, but you get the same job done if you cast Wind Walk on just one. They do decent damage at long range, they have acceptable melee damage, they have tremendous hit points, and most importantly you've invested very little in them so it doesn't matter if they die. What a great idea?! Thank you very much, my friend.