I wasn't saying the Avengers and the Guardians would be in the same film. I was saying Thanos -would- be the A2 antagonist and end up beating the Avengers. After that he would be the villain in GotG...which would lead to the Avengers audience wanting to see GotG in order to find out what happens with Thanos. Warlock isn't the only Guardian that could legitimately take on Thanos...there's also Drax, you know, the guy in the comic who actually "beat" him in Annihilation. As an entire team though they have more to offer than just one guy taking him on anyways...just like The Avengers do. There is no reason they can't all use their strengths to take him down cumulatively.
Additionally, things don't stay secret in Hollywood. They can't be that far along on GotG due to no known script, attached director, or attached actors. The only thing they may be far along with is a concept, which is reasonable but still requires those other things I just mentioned...which we actually do know some of the other films (like Ant-Man and Doctor Strange) have.
Ah, damn. It's hard to keep track of them all. Anyway, they're not going to end the Avengers with the Avengers fucking
losing, are you insane? :lol They aren't going to want to know "Man, what does Thanos do know?", they're going to go "Man that film was poop" and never see a Marvel film ever again. Spoiler warning, because here's how Avengers 2 ends: the Avengers fucking
kick Thanos's teeth in.
Anyway, your second point is null by way of Cap 2 having basically nothing attached to it at the moment either, beyond a bunch of potential directors, the screenwriters and Chris. Likewise, Doctor Strange has nothing for it either. Beyond Thor 2, all projects are pretty much up in the air- Cap 2 could go in like a million different directions. They haven't even said if Sam Jackson is back, or Renner or Johansson or Smulders. At least Thor 2 has a confirmed list of returning duders. Things don't say secret- except when things are too early for anything to leak, just like Cap, just like Doc Strange (they hired writers in 2010- not a peep since), just like Ant-Man and just like Guardians.