I think the world feels more alive if there are people still passing through old content, even if a lot fewer than there were when they were current content. Legion Dalaran in particular is a beautiful city, and as I happen to be hearthed in Astranaar for roleplay reasons, I use it often just to get to Stormwind and occasionally to other locations. Removal of portals from the City of Magic seems contrary to the spirit of the city, and will make it even more of a ghost town than it already is.
Meanwhile, centralizing the portal locations in Stormwind will make Stormwind more dead, not more alive, as people no longer have to travel between the mage tower and the keep to get from portal to portal.
Don’t get me wrong, I like the centralized portal room in Stormwind. I just think the excuse that it makes the world more alive is bogus.
If you want to make the world more alive by nerfing teleportation, start by making the ship between Kul Tiras and Zandalar go on a schedule, so you have to wait until the next ship and then watch it sail out of the harbor and sail back into the destination, like the old ships between Kalimdor and the Eastern Kingdoms. But you know why you didn’t do that: making the world “more alive” is in direct opposition to player convenience, as far as travel is concerned.
A better way to make the world more alive would be to make historical content more relevant. For example, you could take out item level caps on enchants and other crafted items, so there would be more reason to go back and farm old materials.