I dunno, with the way the equipment system works (infinite rings of infinitness) by late game my soveriegn and other champions I've spent gold on pimping out simply walk through enemy stacks like they are nothing. Is it cost effective compared to just buying stacks of my own? No, but its TIME effective. I can get the equipment IMMEDIATELY, whether than waiting dozens of turns to field a decent army. Summons, well, again, I dont bother really. Its more time effective to simply equip my soveriegn and champions.
I think performance, then balance, then AI is the correct priority list.
A suggestion for balance: Let stacks be formed after the recruitment stage, so you can add your champions and sovereigns to stacks of normal units and also to allow you to integrate older recruited units into your forces. This will allow older, before you got the tech for groups/armies units to be effective (single units that are unupgradeable are really NOT effective when stacks start coming out, cept maybe to draw fire) AND it will also allow further choices of where to put the champion, etc. Use the lowest of the stacked units combat speed rating for the units combat speed.
A suggestion for flavor: As you level, instead of just having ability increases, also have a talent tree for your hero you can buy a list of different abilities and traits that effect gameplay. Be that a leadership trait that allows them to lead bigger stacks, or maybe an Inspirational trait which gives an attack bonus to any unit stack they are in, or something interesting like that. I think it'd add a lot of options to character and champion customization. Perhaps even make 'strategic' talents as well, such as ignoring difficult terrain (can move through forests as if they were normal terrain) and maybe a 'Scary' trait that makes monsters less likely to attack their army, etc. Sky's the limit. In fact, now that I think about this, I'll put this suggestion in another post. Its a good idea.
