I carry an old Apple Bluetooth keyboard in my bag. If I was sitting at a table, there were many times that I would connect it to my iPhone to quickly type something out. With the larger size of the "Plus" models, I tend to agree with you for most cases. (And I'm older)
Stick with me here, I swear there's a point that's relevant.....
You may or may not have seen in another thread that I recently changed my desk setup. I work from home full time, even when there's not a pandemic going on, and have been using really old dual Dell monitors that my company gave me back in 2011. Being someone who's always needed glasses or contacts and now has bad reading distance too, those monitors were making me less productive because I found myself hunched over a lot to read small print. My MacBooks, iPad, iPhone, Apple Watch, heck even my car's CarPlay screen all look nicer and are far easier to read than those old dinosaurs I'd been using for work. Which is kind of ridiculous, since I'm using my desktop space 40+ hours a week.
What I ended up doing was ditching my entire desk setup and getting an LG UltraFine 4K. I gave my Magic Mouse and Magic Keyboard to my son and got a Logitech MX 3 mouse and keyboard. Each have 3 Bluetooth profiles. All power, charging, peripheral access, etc. is routed through the USB-C or Thunderbolt ports on the monitor. Basically, it's an exploded-out version of my notebook(s), like an old school 90's desktop computer but way cooler looking and with far less cables. (The mouse I bought makes it really easy to switch desktops in Spaces and has a built in "gestures" pad, so the second monitor really feels unnecessary now.)
The idea of all this is that I can hot swap devices on my desk. The monitor is the where I do "work" regardless of what that work is and what device I'm using it for. This is why I made my iPhone as profile 3. If I've shut down for the day or don't feel like getting out a notebook just to write a two paragraph email, I can pop my iPhone right into that setup, type my email, and go about my business.
This is why I never bought into the theory that the iPad is a modular robotic core or whatever Jason Snell called it. Notebooks with fully matured desktop OSes on them fit that description more than anything, whether or not they have touch screens. With the state iPadOS is currently in (that's not to say it's bad, it just doesn't fit my needs anymore) I really think iPhones and MacBooks fit into my workflow as "robotic cores" more than anything else these days. My iPad largely sits here unused.