Reserving the filibuster for the most serious, important issues and bills doesn't mean there's "one-party rule."    If the minority party is going to filibuster every bill or nomination that they would not have put forward had they been the majority, that is, in effect, one-party rule - by the minority party.   The minority party still gets to vote on all bills and nominations, and when the filibuster requires some serious effort and maybe some sacrifice, the minority party still has that weapon in their arsenal.

As it has been with the push-button filibuster and this current Congress, the Democrats might as well have had only a 1-vote majority in the Senate, because the Republicans have "filibustered" just about anything of any importance (and lots of less important, less controversial things), so even when a sizeable majority of the Senators would have voted yes on a bill, they haven't been able to vote on it.