How do built-in DSP and a phone app make a significant difference with subs?
If he does go the AVR route, he will have Audyssey XT32 which will cinch room issues affecting the bass region up to his chosen cutoff point. Other hardware he is considering may have similar. That is superior to the DSP on the sub, which does not take the room into account – it's only to shape the response of the sub itself. There are other ways to do that, for example Rythmik gets the response they want without DSP.
And once the sub(s) are set up you hardly ever, if ever, change their settings again.
I see these as value-added features that justify SVS premium price, but they are unnecessary. My 0.02.
I agree with you. If I ended up with an AVR, which is probably going to be Denon X3700H, the Audyssey should take care of all required DSP and all I need is just a/two dumb subwoofer. In that case Rythmik L12 ($100 more expensive) could be arguably better than SB-1000 pro (not better than SVS2000pro IMO). But If I ended up with a non AVR system and without a room correction DSP, the SVS DSP would be quite useful for me. It would probably refine some of the most striking bass issues. That is how I am looking at it. (BTW Rythmiks have been on backorder for a while)