People like my wife, who need a lot of screen real estate, rarely have to deal with a keyboard/mouse (so touch works perfectly) and are non-tech enough to get along better with iOS than MacOS, Linux or Windows. She's on her iPad Pro 12.9" 18 hours a day, reading, watching movie or YouTube, editing photos. IOW, primarily as a consumer.
There are a lot of workers out there in the world that need a lightweight way to enter data into forms while they are in the field. They may be interacting with clients / customers in a living room, front porch, etc. Likewise, the lidar features are handy for people like real estate agents who need a cheap / easy way to map spaces in houses / buildings (and I'm sure there are tradespeople, etc who need similar).
There are lots of types of workers who basically look up stuff on the web, respond to email, and maybe answer some kind of chat program. A full on laptop is really more than they need and probably has worse battery life.
I got one years ago to be able to read technical eBooks in a manner that felt closer to reading a real book (ie, a 2 page spread). It's been amazing for that, and ended up being my primary personal computer until very recently.
Content consumers with cash to spare, and professionals who can work around iPadOS' limitations, or whose workflow isn't affected by them. Think digital artists, graphic designers, photographers, writers, some video editors, etc.
Don't forget students. Heading to university as a professional who is employed full time, but I want my own device with minimal maintenance and headaches, as well as minimal distractions. Ipad pro has been a great answer.
Initial notes, drafts, watching lectures, etc is a good use case. Full document drafting in Word is pretty poor compared to the desktop application where I can insert tables of contents, references, bibliographies and integrate with endnote.
The reason it frustrates me is because it doesn't run macOS and I can thus do far fewer things with it. I bought it with that in mind, knowing that the trade-off was that it would go some way to improving my time-on-task with uni. It's been a success in that regard.
In my case, someone who needed extra screen real estate when travelling with my MacBook Pro M1 16”. I set the iPad up on a stand, open sidecar and voila! I have (almost) doubled my screen/work area.
But then lost the option of having a tablet you can take around when you don't need a laptop. Also, if you're developing for ipadOS you've lost access to that. And any apps you may have had in your Apple ecosystem if you were replacing an old tablet.