Is this normal spell-casting ai behavior ?

[Huzurdaddi]

See if you can try the same scenario again but with elemental magic mixed in. The mages should start tossing lightning and fire at the statues instead of summoning, once they get into range.

Nope not at all what will happen. The AI will summon almost to the exclusion of everything else.

Assuming that it has summoning spells availiable the AI seems to cast summoning spells to some threshold and then will start casting some other spells mixing in summons perhaps as the number of summons increases the percentage of other spells increases as well. Not really sure.

But it's simple to see it in action. Take Pythium ( easy to get mages with high level and no fatigue problems ) research evoc-5, alteration-3, and thaumaturgy-6 and script communion, quickness, and some elemental spells and you will see a bizzilion ghost wolves then after a little bit you will see some other random spells once in a while.