Every once in a while the Marvel franchise throws out some outrageously funny movie where you can look past all the plot holes because it's a bit of a laugh but DSMVM was not this and was presented as a serious action adventure.

I think the biggest problem is that the Marvel universes no longer have any rules that the universes have to adhere to. This is a collection of universes where you have Tony Stark and Groot, and witches, and zombies... you literally have aliens and zombies. This is poorly explained as earth 616 + others. Because anything and everything is now possible there is no longer any meaning, it's not madness, it's nonsense.