But it will still failed to live up to the initial expectation. Both BATB and Furious 8 made a billion, and GOTG2 was just as anticipated as those two movies. If it can't even crack 900M then I think it will be disappointing at the very least.
Depends on whose expectation. Only about a third of people in the poll expected it to hit a billion, while over a third were expecting it to end up under $900M. That means the average expectation according to the poll would be slightly under 950M. Which is exactly where it would have ended up if exchange rates were the same now as they were when the first guardians was released. Most people who voted probably had no idea the exchange rates changed and didn't take that into account in their predictions.
Furious 8 or BatB's successes aren't really relevant in this discussion. Did Avatar's 2.7B make the Avengers' 1.5B into a disappointment? Nope, so why would BatB or Furious 8 making 1.2B+ make GotG2's 800M+ less impressive? Clearly BatB and Furious 8 were more anticipated. Furious 8 made more money OS than any superhero movie ever accomplished, just like Furious 7 did before. GotG2 was never going to beat that.