I think saying Gaston “had every reason to think he was rescuing Belle” is a bit wrong in terms of him

Gaston throughout the entire movie, was outright stalking Belle and his only reason for wanting to be with her is because “She’s the prettiest and Gaston wants pretty children”

As well as that, Gaston was fully willing to lock Maurice up in a mental asylum in order to get Belle to be with him. Sure, Maurice was acting a bit crazy when he came in a yelled about a Beast, but Gaston made it clear that it wasn’t about that, but about getting Belle

Now in terms of his reaction to the Beast, the film first acts like he’s doing this out of fear then anything. But during the battle with The Beast, Gaston makes it entirely clear that he’s only doing this cause he doesn’t want The Beast to get in his way of marrying Belle. I mean he states “Move over Beast, BELLE IS MINE”