Assigning different bikes (gear) to different activity profiles. MTB, Gravel, Road, etc.

Same here. It is so annoying that this is not supported. When riding multiple bikes we now have to manually change the equipment used after the activity is uploaded to Garmin Connect. It would be a very useful feature to be able to assign a specific bike to a specific activity. 

If I understand correctly, you want Garmin to assign a specific bike to a profile. How do you propose to handle different bikes for the same profile. Road, I ride more than one road bike, Gravel, my good gravel bike or the winter beater? Hike, different shoes/boots depending on terrain and weather.

We don't want Garmin to assign a specific bike to a profile. As a user we want to be able to assign a specific bike to a profile. Not interested to assign accessories such as shoes or boots although that could also be handled in the same way.  

It can be handled just as Strava does it.  You would choose each primary bike that you most often use for "Road" or "MTB" or "Gravel".  If you happen to ride a different bike for that activity type, then you manually change it for that ride.  Garmin should just do exactly what Strava has done.

I agree with this approach. Strava has a default bike and shoe. Ridewithgps has a default bike. This would certainly work well for most.