Both real-world and on-paper status are literally the exact opposite of what you're describing.
As others have already mentioned, just stating the facts about long-term support: chromebooks have much longer support than Android devices. Both looking at the 99-percentile, the median, and the 1-percentile.
Chromebooks don't get stupid bugs that require workarounds in userspace like:
- BPF maps being broken because someone at Mediatek ran some proprietary static analyser and blindly pushed some fix
- Camera only works properly in the OEM app
- GL drivers are upgraded once every blood moon and very OEM has its custom GL version
- Treble doesn't break because Samsung decided that mount loops were dangerously insecure at a time it wasn't required
- You don't need to keep workarounds for mainline kernels that you can't upgrade, because Google/Android forbids you to upgrade your kernel [1]
Android deprecates driver after 3 years [2], so vendor need to do a lot of work on a very frequent basis. As an OEM, I just want to do my (painful) contributions to mainline, and have them maintain it. Android actively hinders me from doing that.
As an Android OS developer, I could go on and on and on about the stupid issues that Android kernels get that Chromebooks don't. All of those issues would happen just exactly the same on Fuchsia.
I'm not saying ChromeOS' development method works for smartphones, it doesn't. I'm not saying it is desirable, I think it isn't (because it completely kills most innovation). But ChromeOS handles fragmentation better than Android on every single criteria you could imagine.
[1] Google/Android added a bunch a new stupid policies that actually prevent me from upgrading kernels on deployed devices
[2] Yes there is actual planned obsolescence nowadays in Android. It wasn't the case few years ago where obsolescence was accidental