The build quality is fine on the interior, the design of it is somewhat agricultural though and its what put me off it, its not bad quality, its design and material choices you are referring too.Build quality also includes interiors. When we first thinking of getting an SUV we first went looking for Tiguan. Then again in Tiguan subreddit people are complaining about oil leak issues ( which is a major one in Tiguan ). We don't want to end up most of the time at dealer. So we dropped it, we then went looking for a Q3, and we didn't like the interior of the Q3 first as so much plastics in there. And when we did a test drive, I felt the engine a bit stressed under heavy acceleration. Also you won't get HUD/360 cam with a Q3! And the dealer told us, since Q3 is not their hot selling model it takes a year and half to get a new model. We took a test drive of XC40, but the boot space was really small so we dropped that from our list as well. We then went to test drive X1 and we immediately loved it. But I don't know if it was our luck our build got pushed to next year, issues are popping up now as more people are getting hands on, people reporting transmission errors, quality control issues, software glitches. Their new 7 speed DCT transmission is plagued with issues.
All cars have issues at some point. Its just some are more prevalent than others. Ive owned multiple Audi's, VW's, Subaru's, Mitsubishis, and my CX60's have had more problems in six months than ALL of those put together. So build quality is definitely poorer on the Mazda, as seen by the fact they have to line the doors with rubber to make they stop sounding like a tin can, and the suspension starts to squeak after a few thousand miles - this is build quality not pleasantries.
Reliability and build quality is also different. I know the Mazda will fire up every day come rain and shine and its reliability is A1, but the build quality is still poor.