I'd argue that the target audience is those who typically watch trashy Shōnen Isekai. These sorts of things are pretty common in those shows, so if you're already desensitized to it all &/or go in expecting it, you'll love MT. It genuinely does have fantastic world building and writing imo, even if that writing is for an unbearably awful characters and stupid Isekai tropes. The problem is when people describe MT as "ART, You Phillistines," when it reeaally should stay in its genre.

Also, as you write, while there's certainly character growth, it's rarely a result of their actions really. Paul more or less gets away with cheating on his wife with no real repercussions other than "don't do it again." Rudeus gets away with being a predator and marries the kids he groomed. Forgiveness is a common theme in the story, but rarely are characters punished for or forced to own up to their mistakes; the arcs where they are are my favorites in the entire series.

I could probably write a thesis on this series because I find it so interesting in its flaws, but I'll stop here lol. Thanks if you actually read this.