This may work for common phones (aka: Apple and Samsung phones). I had to retire a perfectly workable, but five years old, HTC phone after three such shops refused to fix it, citing unfamiliarity and cost.
I now have an ASUS phone, and fully expect the same to happen in several years.
It seems like weird logic to legislate that Apple and Samsung must make their phones less reliable for everyone simply because a 5 year old phone made by a cut price manufacturer is no longer supported.
Why did you buy the ASUS phone if you don’t expect to get support for it?
I bought it used, and with the expectation that I'm going to be on the hook for my own long-term maintenance and support, as is true with more or less everything I buy. (Full-time Linux user here.)
The sad reality is that the experience of running an off-brand phone with an easily-replaceable battery would, long-term, be much worse than running a locked-in flagship that LineageOS builds for.
They can't really say Apple and Samsung have to do this, everybody else doesn't. And they are by far the market leaders, so they sell the most phones ending up in landfills.
I now have an ASUS phone, and fully expect the same to happen in several years.