OK but it exists. And one could quibble as to whether the 10th gen or the Air is the one muddying the waters. The Air is very close in specs to the smaller iPad Pro.
The way I see it is - do you want / need Lidar, promotion, quad speakers, the nicer screen? It's sorta like the iPhone 13 / 13 pro max paradigm. Do you just need a basic iPhone, or are you happy to pay more for a better camera and promotion?
To add on, I feel the iPad mini is mainly geared towards enterprise and institutions that would benefit from a smaller tablet (maybe hospitals?) while the 9th gen iPad is catered at schools (who are more price sensitive). Which is why I am questioning the "good, better, best" lineup when it's pretty clear that Apple is deviating from this in order to cater to as many use cases as possible. Which doesn't seem like a bad thing in itself given that, as has been pointed out above, the company happens to be managed by a supply chain wiz who should be able to minimise the parts and components they need to order.
I agree the old Apple wouldn't have done this, not because it made bad business sense, but because they simply didn't have the bandwidth for it back then. The Apple of today does, and so they do.
As to why the "air" branding exists, possibly because you already have the base iPad, so you can't have just iPad (the current iPad Air) / iPad Pro. So you need a name for the iPad in between the base iPad and the iPad Pro. Hence "Air" just for a familiar suffix, even if it really isn't all that thin or light.
Give it another year or two, but I find that Apple's product lineup remains fairly lean for a company of their size.