I haven't read Saito's books, or looked too deeply into degrowth as a movement. I just read this article and thought it made some good arguments against what it claims are Saito's understandings of Marx. I'm not sure I agree with everything, but I thought it was interesting enough to share.
I have found the first Jacobin article where I don't want to spit in the face of the author.
Basically what you said in the post's body paragraph is the opinion I have after reading this with the addition that should what this articles authors claim against Saito in regards to distorting Marx should be the truth, then that is an incredibly damning statement of credibility to Saito's work.