profiles are top down, the higher up a quality is in the list the “better” it is. so if 480 is ordered to be “better” than 720 then sonarr will download a 480 version if it sees one even though it may have previously downloaded a 720 version.
the way you have it is typical for most people because they want the higher quality and have the space so dont care
for some shows you really dont care too much and just want the episode regardless of quality. for those i use my SD profile which has the order inverted like this
[X]460 <- cutoff
[X]720
[X]1080
that way i get the episode no matter what. every now and then i might get a 720 or 1080 version but if a 480 version ever turns up later it will get downloaded and overwrite it as its “better” in that profile