Understandable. They mention usb-c transition being the reason to upgrade... but later realized that wasn't a good enough reason to upgrade.
I prefer to be proactive... I wouldn't wait until it no longer works properly, I'd wait for a good deal to come around to replace it. Because $450 seems too high... when it's smart to jump on board when the price tag is discounted.
Sometimes, I feel it’s better to wait if you’re still able to than to make do with whatever’s available.
When my iPhone 7 was starting to get finicky, I opted to wait for the SE2 instead of settling for the (still overpriced) iPhone 8.
When I was starting to get frustrated with my 2017 12.9’s performance, I also opted to wait instead of settling for the 2020 iPP (which was basically the same as the 2018 iPP).
I’m very content with both those decisions. With the iPhone, I saved quite a bit (~$300) and got a better device to boot. With the iPad, I did spend more but I expect M1+16GB RAM will have longer useful life than A12X/Z+6GB RAM.
Maybe when the OP upgrades, he can get a cheaper Air 5 via Apple refurb store at similar pricing to 10th gen now. At around the same price, I’d choose the Air 5 any day over the iPad 10th gen.