I would think adding fx would be preferrable to giving up what the KPA has, which is the ability to deliver the best rendition of great amps.
As for an eq section that models how each actual amps tone stack works? I don't see the advantage. That might be because the eq section of most tube amps aren't all that good. To my ears, the eq sections in the Kemper are far more usable for dialing in or out something which is missing.
Then again, I was never the sort to adjust tone knobs on any amp I really like to use, once I had the tone I wanted. Once it was in the zone for me? I'd never touch it again unless the acoustics of the room or venue were really odd. YMMV.
I used to be like that when I used real amps. I'd set each channel up as a "preset" and just switch between them in conjunction with some sort of effects patch change to sculpt the sound.
Then, when I started using modelers I found that you can often get some really amazingly varied tones by messing with the eq sections. Is this true to life? Not sure, but useful. One some amps more than others, but still useful. I imagine when profiles are made, several tone setup variations are made per amp? I hope so! So much variation between guitars and what not... it would make sense. In other words, if I found an amp I dug and profiled it, who's to say you'd use the same settings? Same mic? Even the same mic placement.
Of course I may find this is all silliness and be fine. I just thought I'd throw it out there as I've read reviews that said they missed this feature that modelers have and the Kemper does not. Knowing how much I lean on it I was wondering if people did things to fill this gap.