I don’t necessarily think it is one or the other. I have just purchased my second pair of hearing aids so its possible that I had an unusual experience, but my first pair are still working after 6 years. So I don’t think that is planned obsolescence - but I guess that depends on how long you think they SHOULD last. I could have continued to use my old ones, but they needed some physical repairs (that did not affect the functioning) and the way my insurance works anything I spent on repairs would be deducted from what they would reimburse for new ones in the future, so I decided to trial new ones. So I don’t think that it is fair to say the manufacturer was trying to get me to upgrade through planned obsolescence of my old ones.
Likewise, to the question of whether or not the newest models are that much better, I think it depends on the timeframe you are looking at. Over 6-7 years I see a HUGE improvement - although I have also switched manufacturers and style, so who knows what is causing the improvements I am seeing. Year to year, probably not, but are people upgrading every year? If so I would guess that they are upgrading because they want to, not due to obsolesence.