Describe the bug
The Portals in Bel'ameth show on the map before the party is over, but they are not there until the buildings appear

I guess that ALL alliance portals for this night-elf druid in Amirdrassil are locked behind quest 76283 , but i have not tested it outside the Stormwind Portal right near the center of the map.

Do you mean these portals?

I have not completed the quest 76283 on my alliance druid and i could use the portals, but I had completed this quest on another horde character. In a Youtube video I watched about this quest, I could see that the portals were there when the player finished the quest, but I don't know if they were there before he finished the quest.

yes and the one north of there.
There is a phase where you have no buildings with any portals there and can't use the portals. So i assumed it is the party that unlocks them