Yeah, I also always wished that some of the animals in Redwall would be portrayed differently, such as, like you said, a good fox. The reason why Outcast of Redwall is one of my favorites is because of Veil, a ferret who was found and raised inside Redwall. He had a lot of naughty habits (stealing, trying to get revenge by poison), and was eventually banished from Redwall, but in the very end he showed that he did have a good side after all. The Taggerung is my favorite also, though it's kind of opposite, where the protagonist is raised by the bad guys but always had a "good" heart, though he's an otter which is typically a good guy species anyway. In Salamandastron (I think?), there was a rat who turned good after he and his partner stayed at Redwall for some reason or other.
But yeah, I do agree, though I don't really take much issue with it.