@C-Jor-El I’m with @Rhodgie on this. You have articulated several reasons why the Ioniq 6 would be unsuitable for you, and that’s before we even get on to whether or not an EV is right for you. Getting money back on the AP is a very poor reason to justify the change and my sense is that you’d soon regret changing the car. As I often say, order in haste, repent at leisure!
You are only a year from changing, so less than that before you can order. I’d just be keeping an eye open for something more suitable that might come onto the scheme between now and then. Whilst the scheme is a shadow of its former self, there are still the odd pleasant surprises that crop up.
As for size, it depends on what you are used to. I’ve had 3 x BMW 5 Series and never found them to be particularly big and it was a very nimble car to drive (other than in snow, when it was hopeless). However, I had a 7 Series once and that was a complete pain to park due to the appallingly narrow parking spaces that we have in the U.K. (my wife was never with me in that car so I wasn’t using disabled spaces).