Imo a weak argument.
“Software updates as long as device is supported” is one of the selling points of SailfishOS, as well as AlienDalvik. And Sailfish is not the only mobile OS offering privacy.
When i bought the Sailfish License it was not clearly stated that the AlienDalvik is not included in the statement.
There is an official Android 9 rom from Sony for the XperiaX, and the Hardware is still fast enough for good usabilty, so if i switched back to Android i could use my device way longer.
I never had to switch a smartphone because of hardware failure or hardware limits, it always was because of software limitations, meaning no more updates.
On some devices i could help myself with custom roms to expand the devices lifespan (Even on a Windows Phone one, the Lumia 1020 which i upgraded via custom rom to Windows Phone 10).
“pretty normal” is quite relative.
Not beeing able to use functional hardware solely because of software limitations / no abilty to upgrade should not be normal.
On a PC it is normal that you can even install Windows 10 on a ten year old (or even older) machine, with some Linux distributions you can go even further back and still have a useable current OS.