Which I personally see as kind of non-sense. Why hold a big and heavy device but limit the usable screen size software wise?
(I do not want to start a debate!)

well, it's either that or 6+" all the time.
I'm doing a lot of daily work on the phone ATM because I don't actually have a choice and for excel even 5.5" is not something very practical. Sure, just as a phone 4" is just fine but for anything else it is not.

I always said a 2016 era slim 5.2" phones was as big as I would tolerate, for exactly that reason: one handed use.

However, while i still have the same requiirement, the march of progress in thinning bezels and slimming screens means that I'm quite comfortable using my wife's Xiaomi MiA2 with its 6" 19:9 screen.

Looking forward to the XA2 Plus turning up in the UK at a REASONABLE price.

I took some photos with Xperia XA2 and X Compact. Both were running official Sailfish OS 3.0.0.8. I used the patcher provided by G7 with X Compact for official build. In my mind the photos are sharper and better taken with X Compact. Take a look of the shoe photo for example.
Inside pictures: link
Outside pictures: link

Without knowing where the focus lies on and where it should lie on, it's hard to judge. The shoes look a little bit sharper on the the X compact. But looking at the door it shows a complete different thing. The writing on the door is sharp on the XA2 photo, whereas it is unsharp on the x compact.

So in the end for me the pics are only showing, that the autofocus still has some room for improvements.

Word pichlo, WORD!
Since what you need is provided, changing to a new device just seems cosmetic to me. Better performance, better battery better bluetooth, all nice but the latter would need ages of work to be perfected as it is on Jolla Phone. All comes down to that simple question: Are your needs met? and will this change give you that satisfaction?