>>213374212
What it boils down to is the villains didn't have any life to them. Galactus is just some big lumbering sad giant. Surfer is some somber silver chick.
No energy to the villainy whatsoever. And the MCU has had some great villains, and the movies with them have always made bank.

Apparently Gunn took this secret with him when he left, because Luthor was full of human energy. You really wanted to see what that fuck was up to next.
Pic related is what WB considered a "good supervillain" before Gunn.