Yeah but even AOU was an enjoyable movie and that's really the thing here. BVS was dour, miserable and so when it had bad moments they stuck out but even though AOU wasn't the best movie it was still fun.
I actually kind of thing Phase 3 will be the best. Shane Black, Whedon and Taylor did the Phase 2 films that people don't think are to the 'Marvel standard'. Marvel Studios then split into its own entity and the casts for the upcoming movies (Ragnarok, GOTG2, Spider-Man, Black Panther) are really fucking good and I'm sure the non-returning directors will do some great work, Dr. Strange has already surprised us all in that regard.
Also, I think this idea that Marvel has 'luck' is really peculiar. Their films are well received because critics like them and audiences love them and not because they just mashed shit together randomly and audiences did an eenie-meenie-miney-mo at the box office. I mean, Marvel may make a shit film eventually but I can't see that damaging their brand as opposed to that specific character who can them be redeemed in a future team-up like Hulk was (Avengers made him so many people's favourite - and Hawkeye shared a similar experience in AOU).