The buckle in a wheel only needs to be small to take out bearings. A small variance at prolonged speeds puts a lot of vibraitons through the bearings. So I am told anyway, and it made sense to me.
I call shenanigans on that, having run slightly buckled wheels for at least 18 months each on two different cars in my yoof and never taken out a wheel bearing I'd put it down to a poor quality replacement bearing, especially as you can't even see the buckle by eye. Can you feel the vibration from it like an out of balance wheel?
As replacements go the cheap Chinese ones last about 1 season if we are lucky (but we buy in a stack of 10 and replace then regularly) in our racing lawnmowers where a decent RHP or SKF will do 3 easily.
I completely agree, i had a pre-buckled one on the back for five years and 60000 miles without issue, this was a wheel nobody could balance as it had a visible flat spot when spinning. I do agree in theory it could damage the bearing but its just sounding all wrong in this case. Think of the hammering that bearing takes every time you turn a corner and put it under load, literally tons of force is bearing down on it normally they last a very long time.
Replacing a bearing sounds easy but requires a good quality bearing and some care. Also you made it sound like you had multiple bearing replacements early in the thread, now it sounds like you've only had it done once and that could easily be bad bearing and/or fitting.
If you can't see it I don't know how the MOT found it as they don't check anything in rotation. So if it is not visible I'd doubt it is that serious, additionally you should feel it somewhat.
97 GT LTS-1
99 GT Lobo DH 1000 x 2