For me personally, it's my travel machine. I've done all sorts of things with it on the road. From SSH to using Photoshop to make some last minute edits. It (barely) fits in my pockets so I don't even need a bag for it. Probably my favorite machine ever at least in terms of form factor.
Screen size does seem to be a personal choice. For me, I've always liked small screens for portability. I'm the weirdo who actually got work done on the first gen Asus EEE PC and didn't mind it. But I can understand that wouldn't be for everyone.
My normal international travel load-out is a backup smart phone + an 8" LTE tablet with eSIM + bluetooth keyboard. It's about as minimal as I can get while still having a real keyboard and functional screen size to handle travel logistics.
I guess you don't know many pilots? :)
This is the app they use https://en.m.wikipedia.org/wiki/ForeFlight
For your second, I think you don’t understand why people buy/use iPads. First off, I don’t really know anyone who uses an iPad mini for anything productive (other than as a test device). A 7-9” screen is just not useful compared to a 13” iPad for things like Sidecar or reading sheet music in live performances. The 7-9” screen being an unfolded phone doesn’t change this.
A folding iPhone could eat the iPad mini, but that’s never been a cash cow for Apple or something power users cared about - it’s more of an “iPod touch” for kids. (And frankly, the Switch 2 kind of obsoletes it.) The thing that would eat 13” iPads’ lunch is something more like Apple Vision.