If the Presidency was an open seat then I can see the Biden rule applying. Since Trump is running for reelection, the Biden rule doesn’t apply.
Biden made his pitch when Bush Sr. was running for re-election. McConnell held the seat because he could. It’s all about power and position (Which is why some Repubs will object to any nominee), anything these people say is bull feces (Especially if what they are spouting is not a codified rule or legislation).