Consumer protection laws might help towards things like glued-in batteries, which would already be a big win (but then again you have reviews that praised Samsung for getting rid of theirs as if that was a net positive), but they aren't going to help the software side of things.
If the manufacturer comes out with version +1 and +2 of their OS that still do run on your device, but coincidentally run only badly enough to make it really annoying to use, how can you protect against that? Even if you mandate that any future version of the OS released during the warranty of your device must run on it, you can't mandate that it runs as well as the original.
When new releases come out the manufacturer will just say that "due to all these new features we can't keep the same level of performance on the older devices" and the software ecosystem being incentivized towards moving to these +1 and +2 versions makes holding onto them even more difficult.
If the manufacturer comes out with version +1 and +2 of their OS that still do run on your device, but coincidentally run only badly enough to make it really annoying to use, how can you protect against that? Even if you mandate that any future version of the OS released during the warranty of your device must run on it, you can't mandate that it runs as well as the original.
When new releases come out the manufacturer will just say that "due to all these new features we can't keep the same level of performance on the older devices" and the software ecosystem being incentivized towards moving to these +1 and +2 versions makes holding onto them even more difficult.