Or those smart enough to root their device to run a "post market OS" such as LineageOS or postmarketOS. Though the caveat of rooting your device could arguably be less security.
I wouldn't expect any 'normal' user to go though any of this. This is for Android enthusiasts that can get access to good hardware on the cheap and run the latest software.
It isn't at all ideal; it is a hack around the problem of terrible software support in the embedded computer industry. Once you got LineageOS on your phone, you can use OTA updates.
I know, and I very much dislike that as well. That is one of the reasons why I got a Fairphone 2, with long term support.
I also bought a Xiaomi for my partner (cause the FP2 would be an old SoC for the same price it cost 2 years ago) with specs which otherwise would've cost us more than double. I expect the device to last 1,5 years. Hopefully by that time the FP3 is on the horizon.