Not sure I understand the term "quality" here. I admit that the turn signal chimes are weird, seats are fine IMO (wife actually likes the CX-50 seats more than her CX-5). Seat belts, I don't understand. But chimes and such are software things that will likely be the same in all new Mazda designs, like it or not.
Now some folks have reported quality issues with the CX-50, but my car has been rock solid (knock wood).
The seatbelt chime is really annoying on the 30 and 50, going off even if you don't intend to drive the car. The 5 doesn't nag you until you start moving more than a few mph.
Then there's build quality. I'm not saying these are "issues" in the sense that they'll become fixes for you. It's just the overall feel and user experience is lesser. The seat belt in the 5 is a silkier, higher quality material. And when you reach back for it, there's an indentation for your hand to slip between it and the side panel.
On the 50, the belt is rougher and doesn't slide as well, and when you reach back for it, it seems they didn't put the same thought into the ergonomics: the belt is against the panel and it takes extra effort to grab.
The speaker boxes are tacked between the A-pillar and door rather than integrated, and could be pushed around when I touched them. Opening the door means grabbing a vertical plastic handle that's far forward on the door. The 5 in contrast greets you with extra padding and is positioned where you get a better lever effect, reducing effort. There's also no surface in the 50 doors to pull the doors closed with, forcing you to use the awkward handle.
And there are more things, like the move away from independent rear suspensions, but I don't need to keep going. I just wanted to add more detail to why I don't like the direction Mazda is going with these new platforms.
Yeah, well that's the trade off, right? If you firmed those things up on the CX-5, you'd probably improve the handling to that of the CX-50, and reduce the ride to that of the CX-50!
We shall find out. I'm hoping there are still enough differences that they won't feel the same. The one thing I liked the most about the 50 was how it rotated and handled, and I think the 5 is just more reluctant to do so because of massive understeer. But the 50 gives you a harder ride with the torsion beam.