Joss Whedon didnt complain about squat. He has always been candid about the behind the scenes negotiations and sacrifices with producers. During his work in Buffy he always said very similar things about the fights and negotiations with the network or bosses while he was still working with the same people for next season. It never felt malicious, mostly because he also has always been very sincere about his own mistakes and shortcomings and because he has always admited that you need to keep the people with the money happy without selling your soul.
The same time he was saying all this, he was saying he hoped to keep working with Marvel cause he loved these guys. This is nothing new coming from him. Listen to his Buffy audio commentaies. Its just so unusual for a director to be this candid taht it seems more than it really is.
And believe me, he has complained about things before, sometimes, in my view, rightly so, sometimes not so rightly and not very profesionally. But this, in my opinion, knowing his public persona track, aint one of them. This is just honesty without malice, wich is refreshing.
Nail, head, etc. All this talk of Whedon complaining is nonsense. All he did was honestly mention the give and take of the studio process in one interview (unless people can point me to more) which was relevant to the question asked. Whedon's been nothing but courteous toward Marvel and he'll likely continue to enjoy a good relationship with them in the future.