No one is going to see the threat as Avengers-level if all of the Avengers aren't involved.
I see a lot of parallels between DS1/DS2 and Thor 2/3. The sequels in each case are a team-up of two main Avengers (Thor/Hulk vs. Dr. Strange/Scarlett Witch) and the introduction of another hero (Valkyrie vs. Miss America).
Conveniently, DS1 and Thor 2 made virtually the same their first weekends.
Due to the events that have happened in the interim, I'd say that Thor: Ragnarok's gross is the floor for DS2, but I don't think it goes too much higher than that. I'd be very surprised if it goes above $150m.