How is that even slightly relevant? The amount of money someone has has exactly zero to do with anything other than the amount of money someone has. It doesn't mean he is a better person, it doesn't mean he necessarily earned it, and it doesn't mean his work is any good. It somewhat implies that his work is popular, but even that isn't necessarily true, and just because something is popular doesn't make it immune to criticism. This is seriously the worst argument I've ever seen.
Edit: Perhaps even more to the point, Bleach is a children's manga. Dora the Explorer* is very popular, but nobody is claiming it is a literary masterpiece. I'd be a hypocrite if I were to read Bleach but claim adults can't like works primarily intended for children/teens, but come on. How much money something makes doesn't really have to do with how good it is.
Edit 2: Or how about Pablo Escabar, who I'm pretty sure was quite a bit richer than Kubo? Are we to determine that because he made a lot of money cocaine is a good thing?
* I'm not up to date on what is popular with kids, but my cousin used to watch this.