Syncing activities/daily HR/fitness status across multiple devices

Garmin fitness devices are not designed to be fully featured interfaces or clients for accessing the Garmin Connect service. You may be used to being able to grab any computer, tablet or watch to check your Gmail, read your files in Dropbox, or even access Garmin Connect using either a browser or the Garmin Connect Mobile app, but that's not what the Edge and Forerunner devices are for or could do.

There are some activity tracking information that can be shared between the devices - read more on Garmin's site or on DC Rainmaker's site - but in general it is as ASmugDill says.

I can't agree. It is like saying that servers were not designed to sync with multiple email clients. It is not a long time ago when Garmin added the possibility to use GCM with multiple devices at the same time. There is really no technical restriction that would prohibit merging the daily HR from Forerunner watch with HR recorded during activity. When the fitness info is not synced from all devices, then the result is nonsense (or at least unusable). I hope Garmin will improve this and add the activity HR to the daily HR and hopefully sync the activity stats between devices soon.

I noted this in another thread but it looks like at least some of this might be changing in 2018, if this comment from DCRainmaker is correct (he usually has pretty reliable info): https://www.dcrainmaker.com/2017/10/garmin-running-power.html#comment-2514744

You’ll see more/better integration of FirstBeat going into Q1 2018, mostly on the backend for things like cross-device sync between multiple devices (Edge/Vivo/Fenix/Forerunner), as well as site/app surfacing of that information.
You’re starting to slowly see things. Garmin is keenly aware of the gap here and looking to remedy. As they themselves noted ‘it’s impacting our best customers’. It won’t be a switch overnight, but you’ll just start seeing the individual gaps be filled one at a time.

I can't agree.

With what can't you agree? If you don't think the technical limitation exists today – as in the firmware in Garmin fitness devices do not allow them to act as fully featured clients of the cloud-based Garmin Connect service, because they were never designed or marketed to be such – then please feel free to give us the correct information. Are you trying to say the design intent was there, but the firmware is defective in every model of device on the market such that Garmin's design intent is not realised in production units?

Whether you can personally ‘accept’ (oh, but what are you going to do about it?) or reconcile with technical limitations that exist today is not a matter of agreeing or disagreeing.