Software keyboards suck for writing longer texts.
I played a bit with an old chromebook we bought for our kid’s school a while ago, and the browsing experience is definitely better than on my iPad Pro. Having actual arbitrary window management, tabs don’t get lost between the instances, video can actually play in the background, extensions work. The list just goes on and on.
I still prefer the iPad for reading long form and comics, but as the Kindle app is crippled, the overall experience isn’t that far either.
None of those are killer apps.
A killer app is an application that is so unique and so useful that it sells the hardware:
https://en.wikipedia.org/wiki/Killer_application
Web browsers, mail clients, maps / navigation, camera software, photo software, contacts management, calendaring, ebooks, and todo list / reminders software are available on iOS, MacOS, Android phones and tablets, Windows desktops and tablets, and even Linux desktop environments.
Are you really saying that the iPadOS version of those applications is so superior to any of the other competitors that people buy iPads just to use the iPadOS versions?
Safari on a 12.9” iPad is like having an ergonomic MacBook browser. It’s powerful enough to render almost everything the web has (save for chrome specific experiments).
But as mentioned above the killer application isn’t software, it’s the form factor. While I have a decent TV, most of the video content I watch is on my iPad. It’s just more convenient.
To add one more, iOS is powerful but simple enough that I’ve recommended an iPad to most older people I know. They can do almost everything they need on it, and neither of us have to worry about it getting into a bad state like a desktop PC can.
And for most of them, the main thing they use on it is the browser.
It isn't just these applications providing all too common functionality, it is the application centric iPadOS that makes them more than the sum of their parts, also. Apple's implementation of iPadOS and their tablet implementations of these common applications cause each to rise to the level of killer app, and, definitely, beyond all doubt, massively drive sales of the hardware just to use those particular yet common apps in Apple's implementations of them on a tablet. There's no great reason Android on third-party tablet, or whatever is running on Amazon's tablets, can't achieve the same, but they simply haven't. Android more or less sucks. Apple sucks, but with iPadOS + tablet app implementations, much much less.
MacBook does all these better and the rest of your list too with the exception of Camera, which the iPhone does better.
You're just hugely mistaken. iPad has several killer apps, but the one that is probably the most important is Safari, followed by Mail, followed by Maps (and Google Earth), followed by a combination of Camera and Photos, followed by a tossup between Contacts and Calendar, then Books, Reminders, etc. That these applications are not original doesn't matter. The tablet form-factor and iPadOS platform makes them all earth-shattering for anyone who has previously been tied to a desktop or laptop with a conventional OS. Prior to iPhone, it was as it is today in that most computer users were not power users. They used web, email, and consumed media. iPad does all that better than anything that came before. It's annoying for more complicated tasks, but it does web, personal email and displays media better really than anything else available.