I have been playing Oblivion for quite a long time, but I discovered just now that the Jephre spells to summon animals that you get after cleaning the Ayleid ruins with the evil rangers (forgot the name), allow you to use all the spells AT THE SAME TIME, meaning that if you summon one type of Jephre's guardians, and then use another spell to summon a different type of guardian, then the first one DOESN'T DISAPPEAR. So you can summon about 10 different animals who can help you all at the same time. It's not like when you try to summon 2 creatures with the same spell, which causes the first one to disappear at the moment the second one appears.

So I am asking myself: isn't this a kind of cheat spell? I haven't yet tried, but I think this horde will be able to tear to pieces just any game boss, the main character just has to watch without doing anything. What was the point of allowing the player to use all the guardians at the same time?

Do you have a summon limit tweak?

Irrc the default limit is 1, or 2, but you can change that using Wrye Bash.

If not, then it sounds like those spell don't work like normal summons.