No, because devices can be and sometimes are sold with software that is already out of date. The better indicator is how long software support is provided for a device from beginning to end.
If I buy a new phone from the manufacturer and it's already unsupported, that's really bad. I don't care if it was supported for 8 years before I bought it.
Hah. This bit us when I got my mother an iPhone SE (2016) to replace her iPhone 4 a year or so ago. I tried to restore from iCloud backup and it kept failing, and finally it dawned on me that the OS may have been out of date. Skipped the restore, updated the OS, and wiped the phone. The restore worked correctly.
On the flip side, the Apple guys have a lot of patience to deal with my stubborn ass trying to activate an iPhone 4... the non-SIM servers were taken offline years ago so I popped in a SIM and off I went.
Sure but that doesn't change how long they supported after end of sale which wasn't in 2013 but at least until 2017. So ~3 years of software updates from end of sale. Still OK but not anything special.
To not be special, there must be many phones out there getting the same or better support. What are they? Who sells these many other smartphones that have had 3 or more years of updates from last sale?
Certainly not the Pixel phones, they get 3 years support from first launch only, and they're supposedly the gold standard for Android software support. It's pretty much the reason they exist. Yet after last sale support for the 5S matched the Pixel's from launch support, and we don't even know that this is the last update the 5S will get.
You decided to count the days of support in a completely uncommon way that no one usually discusses but decided that three years was ok based on the common way people count, which is since initial release.
If I buy a new phone from the manufacturer and it's already unsupported, that's really bad. I don't care if it was supported for 8 years before I bought it.