I found that the summons in Morrowind were too easy for the budding conjurer to perform, given that actual Daedra are summoned. Most are in addition gameplay wise insanely powerful, especially if several are summoned for a short duration. Nothing else is really needed to kill anything, just summon 6 dremora for 6 seconds and good job on eliminating all the fun of playing a mage.

This is my trivial attempt to fix that. I have rebalanced the starting mana cost of all the summon spells by adding the following multipliers. The idea is that summoning from Oblivion is harder than from the Outer Realms. In addition, relatively, sentient beings are harder to summon.

Summon Ancestral Ghost: 1.25
Summon Bonelord: 1.25
Summon Bonewalker: 1.25
Summon Bonewolf: 1.25
Summon Centurion Sphere: 1.25
Summon Clannfear: 1.5
Summon Daedroth: 1.5
Summon Dremora: 1.75
Summon Fabricant: 1.25
Summon Flame Atronach: 1.5
Summon Frost Atronach: 1.5
Summon Golden Saint: 1.75
Summon Greater Bonewalker: 1.25
Summon Hunger: 1.5
Summon Scamp: 1.5
Summon Skeletal Minion: 1.25
Summon Storm Atronach: 1.5
Summon Winged Twilight: 1.75

What this all means is that at the casting costs are increased by a lot. Furthermore all the normal "Summon X" spells (and the ones you make yourself) require higher conjuration skill to be cast proficiently. As an example, all "Summon X" except for Winged Twilight and Golden Saint can be cast at 100 conjuration for 100% chance. For Winged Twilight and Golden Saint, my tests indicate that around 150 conjuration skill starts making the difference while they can be reliably cast (100% chance) at 200 skill.

In other words, the most rare and strong willed creatures require almost super human summoning skill. As such this makes the alternative schools more effective for killing while still keeping conjuration handy for protection, while at the same time increasing the value of mods such as 'Blasphemous Revenants'.