Actually, the Judiciary Act of 1869 set the composition on the SCOTUS, at 1 Chief Justice and 8 Associates. What you’re suggesting is overturning 162 years of precedence and settled law. But, as Bill Maher said, the young are the most gullible generation.
Precedent is a shifty concept though, isn't it? In 2016, McConnell overturned prior precedent with the Merrick Garland nomination, deciding that the president's power to nominate SCOTUS judges shouldn't count in an election year. In 2020, he didn't abide by the precedent that he declared, instead allowing the sitting president to fill Ginsburg's vacant seat as quickly as possible before the election. What precedent is really being set here? That when it comes to a prize as valuable as a Supreme Court seat, the Republicans will do whatever they have the votes to do, not what they have the precedence for. Why shouldn't the opposing party follow that
precedent? Much more convenient, wouldn't you agree?
And maybe it would be a good thing, too. If there were more than nine seats to go around, or each seat had a limited term, maybe we wouldn't see a Senate-breaking apocalyptic political battle every time one of them comes up empty. McConnell's approach toward toward SCOTUS seats destroys the attitude of compromise, comity, and restraint that he claims to be valuing in his defense of minority rights e.g. the filibuster.