To me I find the 10.2" screen to be the sweet spot, but I'd take a 9.7" as well. I have a 12.9" Pro that is quite aged, and a iPad 8. I find myself using the 8 probably 90% of the time. It's so much easier to manage, and I prefer its shape. Speakers are a downgrade, but a small price to pay for what is mostly spoken word listening. The 12.9" is really a beast in your lap or when sitting on a couch, I find this better on a stand or smart cover propped up at all times.
What really gets me however, and this is perhaps leaning into the niche, but I want the proper 4:3 aspect ratio. Only the 12.9" and the home button models have this proper aspect, and I love it. I find document viewing in portrait to be better, and for my old shows that are presented in 4:3 it is splendid for them to fill the screen. Landscape in general feels slightly less cramped, but it is not a major difference. The current aspect ratio is not as Preposterous as the old 16:9 Samsung type tablets, but I will still prefer the 4:3.
I love this iPad 8, but I will probably upgrade it in 2024 or 2025. I suspect the iPad 9 is going to be discontinued within the next two months (or next year at this time) and probably will not be replaced with another home button model. I fear the base iPad price will go up permanently. It may be lower than the current retail price of the iPad 10, but it will not be quite as low as the 9 and earlier. Regardless, I feel upgrading from an 8 to 9 at this point is pointless, at least for me.
I will probably buy the iPad 11 or 12. I have no need for the features of a higher end model, as I've clearly seen with my abandonment of the Pro. Laminated display is nice, but other than that 'hollow' sound when tapping I never observe the difference. The iPad 8 still has a splendid display to my less critical eyes. An SE option as you describe would be excellent, and very good for the education market, but I fear that the time for those smaller models has gone, it's either a mini or a 10.9"+ screen.