It is not a very good idea to make a summoning mage, but if you have some other useful skills too, then it's OK. Why? Simply because at the end where you are to finish off the black ring, there are very many strong enemies, and your summoning skills will be useless. The best that you can summon (without any special item, is probably a level 38 dreadknigth, which will be killled by several others in the BLack Lake (the place where the black ring is). BTW my tactic was (throughout the game) if a strong enemy came, i used skeletal wall, demonic aide and freeze(if possible) on that creature and then(while the skeletons and knight were distracting) i simply used lots of meteorstrikes/lightning or just bashed the guy up. And if you haven't been to the wastelands yet, the know that it is the best to have some unused skill points left when entering them, cause you will have 8 very-very good skills available, for instance divine death: kills the enemy if it hasn't got spiritual resistance lvl1: more then 10, lvl2: more than 20 and so on.
What my point is: it is very good to have summoning skills, but only these won't help you out.
