Since 2015? Easy: Norway, Poland, Greece, Netherlands, Ireland, Singapore, USA probably.
But I do anecdotally agree with your point as a whole: it feels like there has been a slowing or potentially reversal of progress. Perhaps to be expected given the pandemic though.
Easy? You've lived in each of those places for more than a year around 2015 and around now? Physically impossible.
My second homebase is in one of the countries you named. I can tell you that not even 10% of the population would agree with you. Across the political spectrum. No idea that you're basing it on. Crumbling infrastructure, housing worse than Canada, ever increasing problems with immigration.
The US I could potentially agree with, it is the outlier, though debatable.
Ireland I talked about.
Norway is laughable to bring up, sorry. Might as well bring up Saudi Arabia.
If you'd been to Poland and Greece you'd know they're nowhere near "similarly wealthy" countries wrt Canada, entirely different tier. This reveals you haven't really spent time there.
Singapore is a city-state. I'm sure we can find a city in Canada that's doing better. And from what I know, Singaporeans too are majority unhappy with their country compared to 2015, so not sure what you're basing it on.
But I do anecdotally agree with your point as a whole: it feels like there has been a slowing or potentially reversal of progress. Perhaps to be expected given the pandemic though.