Most recent relevant example is the 12.9 inch iPad Pro mini LED screen (A device I also own). Everyone was going bonkers over blooming in dark environments and returning them in masses. It bothered me for about two weeks and now I don’t even notice it anymore. Reality is if you nitpick enough, every device has its flaws. You just need to learn to live with once you are OK with.
I think generally people are very spoiled by how good and flawless iPhones as devices have become. I have a 13 Pro and I’d be pretty hard-pressed to see if anyone had legitimate deficiencies they can spot any device of that caliper and fit/finish. It’s a device that you know Apple hasn’t skimped on in any fashion whatsoever due to the sheer amount they produce. iPads in general tend to be built around a certain price point – probably the reason why even the 12.9 iPad Pro doesn’t have 120 Hz OLED screen with 1600 nits of brightness. A device like that would’ve cost $2000.
I don't quite follow what any of that has to do with the comments about form factor of the new iPad Mini.
You said this:
Every time Apple releases a new form factor for an existing device, there’s always a huge swath of people that return devices for some reason or another
And I countered with the point that I've seen basically nothing but praise for the new iPad mini form factor and it doesn't really seem to be a cause for returns of the devices.