Okay so I’ve done the 3 zones of Zandalar. And now I’ve been sent back to Voldun to blow up some archeological dig sites. I’m on ‘Keep Combing’ quest at this point. Is this still the requirement for Tides of Vengeance or have I been sent on a tangent?
You are on the right track. The quest you listed is from the “Blood on the Sand” segment of the Ready for War Achievement. (Which is needed before you can start Tides of Vengeance.) You’re still pretty close to the beginning of the War Campaign, so you have a fair bit of questing to go.