This is exactly what would happen
Supes n doom have a grudge, they go at it, Shazam being Shazam instantly teams up with Gladiator against DS.
DS wrecks Glads but has trouble with Shazaam
Supes gets Ko'd as usual, Doom grabs glads when he's not looking and rips his head off. Then goes after Seid knocks him out cold
Shazam does some vodo on doom and wins