Not saying there isn’t a market for big gigs down here but places like the O2 are set up to run events on consecutive nights with parking, trains, etc.
Hove (station) and surrounding area is very different to Falmer (station)
Amex isn’t viable for the reasons stated plus there’s hardly any time to stage such an event.
From the other side, why would a big band, star, event, etc want to come to Brighton when O2, etc are just up the road?