The value of the iPad's iOS roots has, for me, been its simplicity. For the longest time, desktop software has always struck me as being overly bloated and complicated (because they sport way more functionality than I will likely ever need). Yes, maybe there are other people who do need that much complexity, but I don't. As such, I wasn't getting more of what I wanted, but instead being saddled with more issues to deal with.
The hardware incentivised developers to create apps optimised for touch and direct input. I can give a few examples of how the iPad has been better than a laptop (or even a laptop + smartphone combination), again, for me.
I remember when I tasked with blogging about my student's experiences overseas (this was about a decade ago). I brought my iPad 3 along with me. The Wordpress app made it easy to insert photos (courtesy of the iPad's camera), type some text and post to my school blog (which at the time was still hosted on Wordpress). All in between the pockets of free time in between. I could do so on my phone, but the 4s and 5s at the time had pretty poor battery life (they would die before noon). The iPad had ample juice to tank an entire day of usage. More convenient than going back the hotel, then having to export photos and writing your blog posts, while dead tired and wanting to just shower and sleep.
iOS apps are often criticised for being "baby apps". It's not inherently a bad thing for something like say, iWork's or Ms Office to have only 5% functionality of their desktop equivalent, if that 5% is all that I need there and then. I spend less time fighting the interface and fighting the idiosyncrasies of desktop Windows software, allowing me to just focus on say, taking meeting minutes on my iPad + Smart Keyboard. And when I am done, email to my manager directly via the share sheet extension.
I have been using Notability for well over a decade now, and still paying for it. It's can't do a bunch of stuff that PDF Expert can (like extracting pages or editing text), and that's fine by me. I need a tool to annotate on pdf documents in class, and I need it to work and for the interface to get out of my way so I don't waste time fiddling with the UI.
And if I need a bit more complexity (being having to increasingly work with massive spreadsheets and functions like mail merge and vlookup of late due to the nature of my work), well, that's what my work-issued windows laptop and my MBA are for. I don't really see it as overkill. My MBA stays on my desk, my iPad follows me around the house (yay for it finally getting WhatsApp), I am already bringing my work laptop and my ipad to work anyways, I even have a 5k iMac at home that's largely been commandeered by my dad, I will say that managing multiple devices is generally a nothingburger.
The counterpoint is that no other company seems to have made this goldilocks device that is both the perfect tablet and the ideal laptop computing experience either. Whether you are getting a Samsung Tab or a Windows Surface laptop, each comes with its own share of drawbacks and compromised. It ultimately comes down to the extent of which you are impacted (eg: some are happy to have the equivalent of a touchscreen laptop).
I will go back to my original point where I argue that the limitations of the OS are there in part to safeguard the experience that Apple wants their iPad users to have. That experience being convenience, ease of use and battery life.