> As far as I can tell Apple has the longest support lifetime of 6 years, followed closely by Samsung with 4 years of major Android OS upgrades and 5 years of security updates.

Anecdote of Samsung support from a few years ago on a decidedly-not-flagship phone (just straight-up copying from a comment I wrote a couple of years ago—):

In April 2019, I needed to rapidly obtain a device, and purchased a Samsung Galaxy J1 (2016) from a major retailer in Australia. I later discovered that this model had already been EOL for over a year when I purchased it. (It was released with 5.1.1, got its last security patch in November 2017, and was actively unsupported no later than March 2018. The handset should very obviously have been updated to Android 6, if not released with it—Android 6 was announced and in beta 7½ months before, and was the stable release 3½ months before, the handset’s January 2016 release.)