Not completely true.
If you want to use the Eveningstar portal that leads to all the Underdark portals, yes. And, unltimately, that's by far preferable.
However, you can also run to the far south end of Kings' Forest and use that portal
without completing those quests. There's a "camp" there you can tag to make that faster in the future.
o
https://ddowiki.com/page/The_King%27s_Forest
In fairness to you (and many others), those specific instructions are not the clearest in-game.
o
https://ddowiki.com/page/Underdark#Access_and_overview