try as you might to dismiss it but, that punch changes a lot of things.
it'd be like Norrin punching Galactus onto his ass and then proceeding to beat him up.
regardless of whether the Watcher fought back or not (they don't have a pacifist code, they have a non-interventionist code, iirc), Watchers are entities far and away above heralds and skyfathers.
what it demonstrates is that Red Hulk has strength great enough to take on a Watcher, which obviously indicates what Green Hulk will have to reach in the re-match.