Basically, with various perks and whatnot, the frenzy spell (adept) works on level 26 creatures/people etc and below, and the calm and fear spells at adept level work at level 17 and 19, i think, although those numbers may be slightly off. If this coupled with the illusion dual cast perk, i'm not sure what the exact multiplier is, whether it's 2x or 2.2x, then that means at adept, if i dual cast, i can frenzy up to level 52, calm up to level 34, and fear up to level 38.

Correct me if I'm wrong, but aren't most creatures in vanilla skyrim level 50 or below? Thus rendering the expert and master illusion spells USELESS

Now i know the calm and fear spells don't reach to level 50, but coupled with kindred mage and animage-which i don't think show up on the spell's effect thingy in the menu- they gotta be pushing that level 50 boundary at least...

Oh yeah, and the frenzy even has an A.O.E effect, much like pacify and rout (expert level calm and fear spells, respectively).

Just seems strange how powerful you can get at only adept level spells, compared to destruction or conjuration, where you need at least expert for both to deal good damage at the higher levels.

PS: I <3 illusion

Try it out. Go to level 50+ using mainly just adept illusion spells. I'm not saying it won't work, but you won't know unless you try it.

Well, I'm only level 24 atm, but giants and mammoths are susceptible to my spells at whatever level they're at, which comes in handy

I hear you. Let us know how the playthrough goes.