I agree with you. I had a 6 for a few days while my CX5 was getting it's trans replaced. CX5 seemed a lot better driving than the 6, also seemed to have better pickup. The 6 was sharp looking but I came away from it not too impressed. I was glad to be back in the CX5. Just my personal impression.
Owning both I know exactly what you are referring to. Part of it has to do with pedal modulation AND suspension. I notice pedal modulation differs not just between each skyactiv model (Cx-5, M3, M6) but even within the different trims (2.0 vs 2.5, ect.) of each model. Then some 2016 models/trims have slightly different suspension characteristics as well.
That said here's my take on a 2013 2.0 CX-5 FWD auto and a 2016 2.5 M6 auto.
The CX-5 seemed to have better pickup when modulating the pedal a "certain way". Like pressing 1/4 in so to speak. Hard to explain. When modulating the M6 pedal the same fashion yes it may seem more sluggish. Long story short the 2016 M6 has a different sweet spot in pedal modulation than the CX-5 2.0 auto. Once the pedal sweet spot is found in the Mazda6 it will accelerate noticeably faster than a CX-5.
The CX-5 has 17's and the M6 has 19s. The CX-5 has better turning radius and feels really good handling especially for an SUV. Actually feels better handing under 50mph. I wish the Mazda6 came with 18x8's. That said when pushed hard the Mazda6 shines. Hitting corners at 50mph, switching lanes and merging at 70-90mph inspires confidence. I drive to work 4am in the morning and have all the streets and back roads all to me!!! Mostly anyways. The CX-5 has the advantage in stop and go traffic as its more nimble in tighter quarters.
If lowered just 1 inch and with better tires even on the 19x7.5's The Mazda6 would be am even better handling daily driver. They made the M6 (maybe other 16 models too) with softer suspension resulting in a slightly higher stance.
City handling- CX5 >Mazda6
Open road handling- Mazda6 >CX5
