I’ve had my 10.5 for almost 2 years now and it’s showing zero signs of slowing down, it’s still a beast of a tablet and that 120Hz display is a dream to this day; I sometimes turn the option off and back on just to appreciate it more!
I wouldn’t call it a “lemon”, I think the iPad best suited to that badge of honour is the 3rd Gen with Retina Display, a machine that was woefully underpowered and replaced 6 months later as the 3rd gen just couldn’t push the pixels on the display (I bought both).
Reliabilty wise, the only thing I had my Pro replaced for was one of the cellular “lines” at the top of the display started to protrude from the bezel and was quite sharp, so much so that my toddler hurt her finger on it (I know, she shouldn’t have been touching it in the first place before the keyboard parents have their say).
All in all, I’m still happy with the performance and form factor and unless iOS 14 causes major issues I don’t see me upgrading for at least another 12 months or so later.
And when I do upgrade, I won’t be going for an Air or equivalent; once you use ProMotion on an iPad, you can’t go back.