I think the general consternation about Mueller started when he predicted that, as a matter of law, Oracle would ultimately be the victor in it's case against Google over Java.

Which did eventually come to pass, in a Federal appeals court ruling in March of this year that overturned the findings of the jury in the previous trial.

He was paid by Oracle when he made that "prediction".

When someone works as a hired gun, all their good works are tainted as well. So who cares.