The only Mazda that I owned was a Protege about 20 years ago, and I primarily purchased it for its price/value relative to the competition (i.e. Civic/Corolla). While the CX-9's driving dynamics and aesthetics are a major draw for me now, the key drivers are the same - price/value. As someone who will not buy a car with leather seats, that meant buying a 2018 CX-9 Sport this spring with AWD and the Actvisense package - which I am guessing would run me somewhere in the $31,000-32,000 range.
My sense is the Ascent Premium will cost me more (I am guessing roughly $3,000, give or take - depending on the relative discounting by Mazda), but for that I get a pano sunroof, Apple CarPlay, better seating options (either 8 person or 7 with captains chairs), standard roof rails, USB's out the wazoo...as well as a car that has all of the safety bells and whistles, a well-established AWD platform and historically great crash test ratings. I do also worry about the "little things" that some CX-9 owners have been complaining about (infotainment, squeaks and rattles) that - in a vacuum - aren't a big deal in the overall scheme of things, but given the crappy dealer network in my area, will be a PITA to deal with.
At the end of the day it will come down to whether the Ascent is a decent car to drive with good fuel efficiency - which are the key selling points for the CX-9 for me. If the Ascent is even close to the CX-9 in those areas, it will be a very difficult choice for me. I am completely willing to sacrifice some space and utility for a better driving experience, but the substantial amount of things I can get (listed above) in a Ascent Premium - for a reasonable amount of $$$ - will make it a pretty compelling option relative to the CX-9.