An advantage of my 9.7 inch iPad Pro was a huge selection of cheap but highly rated keyboards, the same size I think as the iPad Air, so a huge market. It may serve my purposes well into the future, but everything was so cheap ($260 for the iPad I think, maybe higher now), that I could see upgrading in a few years. I would already have a Pencil, Air Pods, and experience with the latest stuff.
I also don’t need a lot of storage for what I use it for. The 99 cents a month iCloud plan serves my purposes for both storage and backing up the iPhone and iPad. I use other cloud storage services as well, all free. One is Dropbox, with additional free storage for a year, under a special deal. I might stick with it after that, and pay, as it seems that Microsoft’s One Drive and Apple’s iCloud work with the competition (each other), but maybe not quite as well as they could. They each have more incentive to work better with a third party like Dropbox. I use both Apple and PCs.
It was a little odd that that Apple’s Preview pdf tool doesn’t work on the iPad or iPhone, but the third party apps developed instead by others are pretty good (and cheap), and better IMO. It’s getting to where you can markup stuff directly in OneDrive and iCloud using the associated hardware, generally, I think. (But you can markup in OneDrive using Apple iPad or iPhone, I believe, similar to how Word etc. there are free). But all of this is somewhat in development and transition. I thought PDF Expert was going to be develped for PCs as well, but it hasn’t been. Maybe just the Mac? Others are highly rated, but from what I see, most iPad users rate PDF Expert the highest. I also use GoodReader and iAnnotate. Adobe is getting better not not as good as these.