The 2.5T will be faster in sustained straight line acceleration, 0-60, 1/4 mile, etc. simply because of the higher horsepower, but I doubt the difference would be as large as 2s from 0-60. In normal daily driving they will feel very similar. When I drove the 2017 CX-9, it had the most diesel-like powerband of any gasoline engine I've tried. The 2.2D will have more grunt just off idle which you'll feel when casually rolling off from a stop, and the 2.5T will rev out an extra 1000 rpm in the lower gears when you have the pedal mashed. But with either engine you'll spend the vast majority of your time between 1500 and 4500 rpm where they are very close to the same.
I don't necessarily agree that they appeal to different customers. Obviously, there are some people who won't buy a diesel for no other reason than it's a diesel, but who would buy the 2.5T. And there are a few people who are mainly interested in the diesel for fuel economy and who wouldn't buy the 2.5T. But I think there's a lot of overlap between the potential market for the two engines. I'll bet that if we had the chance to drive both of them back to back, most of us could be happy with either choice.
If you want to know what the 2.5T is like, test drive the CX-9. It's not anything like the 2.0L turbos in the Forester and Escape, which are tuned more for high rpm boost and when you mash the pedal you feel the lag followed by the turbo push as the revs build. The Mazda 2.5T is tuned more like the VW TSIs, with minimal lag and plenty of boost at cruising RPMs, but running out of steam as you approach redline.
