I've never used vinted either, so I really can't help with how theirs works or if it's better or worse.  I think people are entitled to complain when something as fundamental as getting a purchase delivered and which has basically remained unchanged since RM started selling stamps at post offices (in about 1840?), is suddenly changed into something more complicated.

I think you meant, ..."ebay switching it to buyer pays,..." ?  Not seller ?

But does it really matter whether sellers like the BPF or not ?

Some sellers who don't like it have stopped selling, others who do like it or aren't bothered one way or the other are still selling and it's some of them saying that the BPF has reduced their sales.  Not those who have stopped selling, whether because they don't want to use SD or object to the BPF, or because they just don't like what ebay has become.

Your idea of a single charge per listing is going back over a decade to the fee structure when I first started selling.  A sliding scale of 'insertion fees' for everyone + FVF.  I don't recall there being any great demand for that to be changed, but ebay changed it anyway.

As for free listings, as you say they were 'once in a blue moon' and when those rare "Free Listing Weekends" were dis-continued, ebay gave private sellers 20 freebies per month as compensation.

Why ebay then started increasing that number, I have no idea, again I don't recall any great clamour from private sellers for ebay to do so., but again ebay did it anyway.  For years my free listing allowance was 200 a month, far more than I ever used (my record number of active listings stood at 20 something) bt ebay still increased it 1000 and then made it unlimited.

It's always handy to have someone or something to blame when things aren't as good as they were and private sellers with free listing and selling are an easy target which most private sellers can't be bothered to endlessly debate.  Did they ask for free listings, free to sell, GTC rolling over listings month after month ?  No.

And don't forget that most who abuse whatever ebay decides to give private sellers, are businesses.