I think the Air started messing up the lineup. And it was totally unnecessary. All iPads have always been light... it's not like they removed the optical drive from an iPad.
I think you're right.
The iPad has always been advertised as 'thin and light' and therefore the Air branding has always felt redundant to me. It felt redundant in 2013, and it feels even more redundant now. The Air is still the lightest full-size iPad but the difference is so small you're grasping at straws really.
Fair enough the 1st gen iPad Air truly was significantly thinner and lighter than what came before, but that was just a natural development of the 9.7-inch iPad and didn't need to be rebranded 'Air'.
When the MacBook Air was introduced it made perfect sense as it genuinely was strikingly thin and it ushered in a new class of notebook computers. It booted out the optical drive and shocked the world with how it could fit in an envelope. iPad Air? Can't say the same. In fact I recall a slight giggle from the audience when Phil Shiller said it'd be called iPad Air.
I'm not a marketing guy. Apple know the sales numbers better than I ever could, but I just think it'd be so much better if the iPad line went something like:
iPad SE (a rebranded 9th gen iPad)
iPad (includes the 10th gen iPad and also the iPad mini. I'd bring the 10th Gen iPad specs up to match the mini and make it compatible with the 2nd gen pencil)
iPad Pro (11-inch and 12.9-inch iPad we know today).
As for accessories, the 1st gen apple pencil would stick around but only for the iPad SE. Apple could market it as Apple Pencil (for iPad SE) rather than the nondescript '1st generation'. Everything else would work with Apple Pencil 2.
Magic Keyboards, Folios, and Smart Covers would work with all full-size iPads with the modern design. the mini iPad and the iPad SE would still need to have their own cases due to their size/shape.
It's still not as streamlined as it could be but at least it makes more sense. In an ideal world we wouldn't have any 'SE' model but I get that Apple like to use that as a way of saying 'the iPad starts at only £369".
Again I'm not a marketing guy and the big price gap between regular and pro would be an issue I don't have an idea of how to resolve, but it should be a lot more streamlined than it is.