Well while the Mazda CX5 GT might feel like "sitting on a sheet of plywood" according to the OP. Here is what happens to GM seats after just 5,000 miles of driving:
Mind you this is in a $70,000 GM vehicle. I've owned GM vehicles in the past and the interiors on GMs fall apart fast and the leather seats in GM cars are pretty shoddy. After 10,000 miles in a C5 and C6 Corvette, my GM seats looked like they were 20 years old.
So much for the "soft and supple" seats. They are so soft and supple that they fall apart after a few thousand miles. I guarantee you the Mazda CX5 seats will look like new after 30,000 miles while the GM seats will look like garbage.