a lot of that loss comes in the front end (not quite as clown-shoed as the Mazda3). Yes, the trunk and back seat are tight, but not appreciably worse than the Mazda3 hatch.
Lady No-san's mother went from a Mazda3 hatch, and then when Lady No-san's father bought the 2001 911 Turbo, his then-current 2014 CX-5 GT went to Lady No-san's mother. She hated it and traded it in early (lease) for the CX-3 - the price difference was something like $11/month saved...the CX-3 is expensive, IMO, for what it is compared to other Mazda offerings. So she now drives a loaded CX-3.
How does she feel about the CX-3? She fricken LOVES it. Absolute love. The old, old folks (90 and 92) find it much easier to get in/out of the CX-3 than it was for both the CX-5 and the Mazda3 hatch, and neither complains of lack of room in the rear seats. YMMV.