Whose job is it, FRE edition

I finally got around to reading the argument in Warger v. Schauers, dealing with whether FRE 606(b) prohibits inquiry into jury deliberations in trying to show that a juror was untruthful during voir dire. During the argument, counsel for respondent (the defendant, who won at trial) repeatedly argued that, if the Court believes it would be better to allow juror testimony on such claims, then it is a job for Congress to change the rule. Counsel repeated this point several times, always mentioning Congress as the source of any change.

But it is not Congress's job, at least not primarily--it is the Court's job, under the Rules Enabling Act. It is true that the original 606(b) from 1973 (it was amended once, in 2006) was affirmatively enacted by Congress as part of the original Federal Rules of Evidence. But since then, changes to the FRE follow the same procedure as changes to the FRCP or FRCrP, with the advisory committees and the Court taking the lead and Congress merely exercising a power to disapprove a submitted rule. And while Congress can always amend the rules through ordinary legislation, that is not the primary or presumptive way to make a change. When litigants talk about the meaning of the FRCP or the need for amendment, it is always discussed primarily in terms of the Court and the committees. I am wondering why it should be different with the FRE.