Hitting just the major story beats in 70 levels shouldn’t really be that hard. You’ll just want to keep it to the main overarching story of each expansion plus a few relevant extras.
If you look at something like just condensing WotLK, the important things you need to cover are:
- Arriving on Northrend to set up bases to fight the Scourge
- The Wrathgate
- Adventurers break off to deal with Yogg Saron(not super relevant here, but the old gods are relevant to the lore as a whole).
- Sieging ICC and the events that happened there.
Plus the connecting quests to make it all flow properly. Sure there’s a lot more that happened in WotLK, but those are the relevant plot points players should be aware of to understand the story going forward.
Hell we could probably even continue going about pretending 99% of WoD didn’t happen since it mostly relates to alternate timeline stuff.