Why would you do maintenance faster than Mazda suggests? i trust Mazda engineers know what they are doing, which is why I bought a Mazda in the first place. I have not read about widespread failures to engines or the power train on Mazda vehicles, is there evidence otherwise? I follow the maintenance schedule in the book, including oil changes at 7500 miles, not 5000 like I read many on this forum do. There is no way Mobil 1 and a Mazda skyactiv engine need more frequent changes.are you sure you are referencing the right service schedule? i don't have the schedule handy but, when people ask on here for the NA models, they are usually told not to worry until much higher mileages about doing the jobs you're worried about OP's friend having missed.
Edit: i think a lot of the maintenance should be done before Mazda suggests; i'm referring to what they suggest in the maintenance schedule.
That said, contrary to the manual, I do believe that differential fluid, transfer case fluid and trans fluid are NOT lifetime fluids and will change them out at some point at or around 60-100k miles.