It makes no difference in their battle against WP Engine, who would very quickly discover which lawyers they're going up against with or without this blog post.
That line in the blog post is aimed at public perception, not WP Engine's perception, and from a PR point of view there's not really any benefit to it only downside - I guess their thinking is that some members of public might think "the winning lawyer wouldn't join the losing team so Automattic must be in the right here", but it actually makes them look like their legal defence is weak enough that they need to resort to trying to win through legal skills rather than business facts.
When I call it "crazy" I'm talking from the point of view of someone who has drafted a couple of announcements quite similar to this one, and many others that weren't related to defending legal cases but were still walking tricking lines in PR/comms, and I just can't imagine a line like that being suggested by anyone I've worked with and can't imagine letting it slip into a release I was involved in.
