No, what they said originally is correct.
You DO need all 3 skylances, and all 3 North ro missions for ToB.
You DO need samples of corruption for ToB.
Saga skins is NOT needed, it is needed only to get the next task.
Nor is preparing your skins.
Becoming the Vessel is NOT needed for ToB, but is needed for Razerthorn access, which is where you kill Sullon Zek for Deathknell access.
So for ToB, I think you just need the 3 skylances, 3 north ro, samples.
For deathknell you need sullon zek, so you will need become the vessel for that, but not ToB unto itself.
Iirc.