[Ultimate Psionics] Just how handicapping is the Psionics Are Different variant?

[EisenKreutzer]

I realise that the Psionics are Different rules variant can open up some rather nasty cans of worms regarding spell resistance vs. power resistance if psionics are introduced in a standard campaign setting using core material.

But what if it's the other way around? If you have a campaign world without arcane or divine casters, and then introduce arcane casters as enemies, who comes out on top? The monsters will have spells and spell-like abilities, but no power resistance. Will the players stomp all over these arcane enemies? Will they too suffer some drawbacks from this?

[Squirrel_Dude]

Besides a complete lack of access to the magical items some classes depend on, and that saving throws and AC rely on to scale up at something approaching an appropriate speed?

[EisenKreutzer]

Besides a complete lack of access to the magical items some classes depend on, and that saving throws and AC rely on to scale up at something approaching an appropriate speed?

Yes, besides that.