This is a good primer: New Discussion Boards Help Guide
It is true that you can see “every post from all users in a slurry” if you want to, which is I guess an increase in functionality from before, though one I gather you are not interested in. I think you will find that the “advanced-micro-devices” tag is a 1-for-1 replacement for the AMD board you knew and loved. Posts from the old board were migrated over with that tag applied, and any posters wishing to participate as before should just post with that tag. If you feel this is leaving something out, could you specify what that is?
Regarding these particular tags, “AMD” is an alias for “advanced-micro-devices”. Whether you go to https://discussion.fool.com/tag/advanced-micro-devices or https://discussion.fool.com/tag/amd, you should see exactly the same thing. This is exactly so that people who think by ticker symbols and people who think by company name will not miss each other. This should be the case for any company tag.