Before, in E:WOM, I noticed that familiars and summoned creatures would be able to remain useful for a time, but at some point because of all of the upgrades that champions, units, and sovereigns were getting, they became less and less competitive.

With Mr.Familiar(tm) at least, his resummoning cost was low enough that using him as a distraction/redshirt while the more powerful units jockeyed for position was an option I took advantage of a lot.  The current summon nature spell still kind of accomplishes this to a degree.

However, I think it might be nice if the 'summoned by artifact' units were more competitive in the level advancement area, so that Annie The Dog might be able to stick around for a while, instead of being constantly wiped out on the battlefield once the stakes/combat stats get more lethal.  I recently parked a summoned Sand Golem in a city in my most recent game,  just so I wouldn't have to bear watching him get wasted almost immediately in my travels, which was a shame.

I would rather have kept my Sand Golem around, if his combat and defensive abilities would have increased through experience/successful battles at a pace that would have kept him relevant, but under the current system that isn't really happening.

Attack ability advancement probably isn't as important, but hit points/defense is something that should increase at a more comparable rate, otherwise said units are just speed bumps in later stages of the game.

It is nice to have units/champions that you grow attached to because they've survived many combats alongside you that are able stick around as you grow in experience, so when they do finally fall you feel like you lost something important, instead of just a throwaway token.