The iPad is the saddest device I know: it's both a turd and the computer I yearn the most for. Extremely well-engineered hardware with lots of potential, let down by a toy OS in terms of what it allows for. It's only as good as its OS, so after all these years the iPad is still a big iPhone to me. Be it iPad Pro or the mini.
Perhaps there's the occasional graphic designer or [INSERT OTHER PROFESSIONAL HERE] who found serious use for an iPad, but I can't see them objecting to being able to do more. Workflows that mean moving between systems all the time are not exactly great. It still is mostly a consumption device, solely because of the OS.
What Apple's (read: Steve Jobs') initial intention/vision was is irrelevant. The single reason we don't have a desktop quality OS for iPad is money: many (myself included) will buy one device instead of two. Any other argument is mute, period. If it made financial sense to put something macOS-like on the iPad, Apple would have. They could have pioneered a new generation of desktop class UI:s ("desktop" referring to OS capabilities, not necessarily traditional desktop-interfaces), but instead chose to shoehorn in desktop-looking features on top of the same closed-down OS. Does "macOS-like" mean too complex for the average user? Apple could have easily allowed the user to set a "simple mode", similar to the current iPadOS. Then again, I feel that's how the Apple Watch started: innovative, only to gradually return to a more tried-and-tested touch interface. Simpler to design for, but not necessarily better. Apple's touch interfaces are also gradually getting worse, and less intuitive.
iOS/iPadOS is app-centric, not data centric. That alone makes it ****, regardless of all its technical innovations. File handling and how we interface with data is crap (no, touch is not necessarily the best interface, but Apple have already acknowledged that with keyboard accessories... Thanks?), and many (most?) apps still have their own sandbox.
My computer's main reason for existing is the data I put on there. Whether creating something new, processing or consuming existing data etc. There's no reason to disallow a terminal, compiling code etc. We can uh "develop" in Apple's Swift sandbox for iOS only - does anyone actually build complex software with that? And while Swift itself seems like a nice language, it's too Apple centric (yes, it matters, a lot - I and many others need good cross-platform tooling) and loses in popularity to many others, for many different reasons. I need to install the toolchain/compiler/interpreter/libraries of my choice and develop with software of my choice. Coding is no longer a niche/"pro" activity.
Apple knows it can't drop the desktop class OS completely (which currently means maintaining the Mac), since for an iOS-only lineup how would we otherwise develop software for Apple devices? On Linux/Windows perhaps... And as food for thought, if Apple were to hypothetically disallow computers "below" MacbookPro to use macOS and make iPadOS the baseline, then what? It would make me move to Linux, thus I now own one Apple device less. Apple need to solve that, since for every Apple device a user drops, the Apple ecosystem and connected services will make less sense, meaning there's less friction in changing to non-Apple products for other product categories as well.
If I were to get a new iPad (my current one died), it will end up as a browsing and comic reading machine with the occasional movie watching during trips. Anything else is cumbersome at best.