Thx vayu, I had a typo. You are totally right that runlevel 3 is in siduction the one without X and systems boot to runlevel 5 with X.
Besides noX, that one boots per default to runlevel 3, which is its purpose. When you now install some DM on top of noX (while being in 3), it then boots to RL3 with X, so my post was about how to change noX to behave like other siductions: take the DM out of RL3 and set RL2 as default.
And as that post above came from tests in a vm that no longer exists, I suppose I confused as well runlevels 2 and 5, 'cause in my siduction-KDE inittab says for default runlevel id:5:initdefault: :wink: