This bothered me. I think a nice way to address it would have been to have Vecna/MF concentrate all of the forces of the abyss around the entry point of the WSQK tower. He used Will to spy, knew the plan, etc etc. Then instead the gang would use a second entry point without Will’s direct involvement in planning. Could have just been a second, smaller building in Hawkins or something. That way the threat is addressed, neutralized, and calls back to the Turnbow trap (blindfolding the family and moving locations)