@Still-learning, some history might help. The OS for the MBA, called macOS, is based on a variant of *nix, which is a generic version of a product developed by AT&T called Unix. And that software was built for keyboard input, mouse manipulation and what you would generally think of as a "computer" for the desktop. (Actually, it goes back to before that, but we'll leave ancient history out.
) The OS for the iPad, of all sizes, is currently called iOS, although in a few days the iPad version will be called iPadOS to differentiate it from the iOS on an iPhone. That iOS was designed for a limited input, originally for the iPhone, where you have a touch screen, no real keyboard, no mouse, no external devices, etc. Although still based at its core on *nix, it was significantly shaved down to fit into an iPhone and support the particular components in that device. Also bear in mind that the CPU in the Mac is an Intel chip, a descendent of the Pentium chip, with the same basic internal architecture and instruction set. But the CPU in an iPhone or iPad is an Arm chip, developed by Apple, with an entirely different architecture and instruction set. So an application developed for the Mac cannot run in the iPhone because the low level computer instructions are different. Even the OS cannot run in the other system. iOS won't run in a Mac and macOS cannot be installed to an iPad.
OK, so the app developers come along and want to make, let's say, a word processor for the iPad. To squeeze it into the limited storage space of the smallest device, they started taking out components. So no keyboard support, no real mouse support, no external devices support, remove some features and tricks that not everyone uses. Then compile for the iOS instruction set and test to see what got broken in the process. Lather, rinse, repeat until the product is sort of usable. The result is that the iOS version is a bare-bones essential system, just barely useful at all. As the devices mature and have more storage space, more work memory, etc, the developers can put things back in. So a keyboard is added to the iOS version of Word, for example, because now you can attach a real keyboard to an iPad Pro. But it's still not identically featured as the Mac version of Word because of the differences in the hardware between the two.
All that means is that to make an app that can be synced between a Mac (or a PC) and the iPhone/iPad is a non-trivial adventure, one that a lot of developers have simply avoided. Microsoft took a long time before the first version of Office products came out for iOS, and when it did, it was a skeleton. Adobe tried Photoshop, again with a hugely reduced edit tool set. Even Apple struggled with Pages, Numbers and Keynote, their version of Word, Excel and Powerpoint. Slowly it's gotten better, but there are still differences.
I'm not sure what the market for the iPad Pro is, to be honest. As a road warrior, I wanted a true portable, not a tablet. The "saving" of space is negated by needing to have a keyboard to go with the iPad for any serious text input, so why not just carry an MBA, or MBP? The flat, tiny keyboard on an iPad is simply not conducive to touch typing, at least for my hands. I guess it is that I have just never seen any business value of the tablet for work, so it turns into a personal preference. He wants a tablet? Great, he can have it. She wants a portable? Sure, whatever makes her happy.
But you don't have to go with third party to get some of what you mentioned. You said google calendar. Well, Calendar on the Mac will sync to Calendar on the iPhone and iPad through iCloud. And it works pretty well. You can also use iCloud or just about any cloud sync service to share documents. My wife and I use Dropbox to share documents we both work on. iCloud will also sync Mail, Photos, Contacts, Reminders, Safari-saved passwords, Notes, and Keychain logins. So before you lash out with cash to get something from a third-party, give the Apple tools a try.