Would GOTGV2 have been regarded as a box office bomb or flop in another era?
The film grossed $863 million on a $200 million budget, so not a flop. However, Disney only collected $383 million from that $863 million gross (the rest going to theaters and in taxes) and the film had a total expenditure of $515 million; it only went into profit during its video window.
So based on one particular criteria (if you're basing theaters as the only revenue stream) this film would technically be a flop for not breaking even at the box office.
https://en.wikipedia.org/wiki/Talk:List_of_box_office_bombs_(2000s)#In_Response_to_Evidence_Offered_by_BornonJune