Yeah, I've never much pushed the boundaries of my iPP myself but there again lots have and your statement in some regards is like is a red rag to a bull, say on the iPad forums, were it not for your very sensible 'mainly' qualifier there at the end.
It is not intended as a red rag to bull, but as an observation. But "mainly" makes sense as such things are not absolutes.
Anyway, in my experience, the uses to which iPads and MBAs (I have the legendary 11" - a maxed out CTO - which is easily the best computer I have had in my life) can be put, overlap considerably but they reach have different strengths.
If you are creating content - a considerable amount of content, especially written content - a computer is far better (or more comfortable) to work with than is an iPad. However, for the consumption of content, and portability, and ease of use in such settings, the iPad clearly has many strengths.
Five years ago, I bought an iPad mini (strongly recommended by colleagues) - actually, over time I bought two.
I ended up giving both away, one to each brother.
In truth, I hated the iPad, mainly because I write a lot - both professionally and personally - and I really need a proper keyboard; the touchscreen (as with my iPhone SE) is okay for short notes and messages, but it is not comfortable for the business of writing. I found that I didn't enjoy them and far preferred my MBA.
My brothers both found uses for the iPads, but still used both desktops and laptops.