I wish this were true.  In fact, when it comes to magic, henchmen can never advance past the 'Adept' stage.  They can never become 'full' mages.

I created a henchman called 'Surveyor' with 'Earth magic' that I was planning to create roads and of course raise/lower land.  It turns out that he could never advance in earth magic far enough to become an 'Earth Mage' which is required to raise/lower land.  I wish they could rise to Earth Mage - even if it cost a lot.

Thanks.  Good to know, but I still would like to be able to train someone who could be an 'Earth Mage.'

or a 1 influence upkeep, should prevent the stack of 1 champion + 8 henchmen, all with shieldwall and experience bonus

Henchmen should definately have permadeath.

I stopped playing Altar because of how unfun it was to abuse henchmen...

Also if you want to equip your "real" champion, another henchman, or your sovereign with a set of newly researched armor or weapon it is also cheaper to just train up a henchman with the armor on.  You can then trade the armor to whoever you want or even sell them.  If you were to buy the pieces from your shop it would cost a ton of gildar, but production is easier to come by.  I also noticed after you trade the armor off the henchman sometimes keeps his defense rating until you equip something else (bug).  The henchman's mount and accessories are not removable but you can equip 4 more accessories on top of what it was created with (bug?).

I do like the concept of henchman a lot, but it seems like they are highly abusable and probably over the top in their current incarnation.   Shieldwall stacking gets out of hand.  I do not think that henchmen should ever be able to buy spellbooks and should be stuck with adept skills.  Also note that with the changes to pioneers costing population, governors on demand are even more powerful.

 Your sovereign should really be the star of your heroes, and your champions should be special too.  Henchmen should be just that, and not be that uber.

Regular trained units can really be the strongest things out to anything without overpower or the blizzard spell.  The issue is that it takes really late game to make them that effective, but champions/henchmen can reach effective armor/attack/health levels without as much tech since you can outfit them with found items.

PS: Pariden should be renamed to "book beyotches."