I am attracted to the argument, made by Thomas Geoghagan and others that the filibuster is unconstitutional. That said, even if you want to accept the view that it’s unconstitutional, it’s not clear what the remedy would be. A case about congressional procedure would be a textbook example of a non-justiciable “political issue” that the Supreme Court wouldn’t rule on. So the claim doesn’t really get you anywhere.
I think the more relevant point is simply that contrary to what’s widely believed, filibustering is untraditional. Or, rather, the authentic tradition is that white supremacists would throw a hissy-fit when faced with civil rights legislation. On other controversial issues, from tariffs to FDR’s court-packing to the whip count for Medicare, everyone took for granted that a majority sufficed to legislate. The idea of a routine supermajority requirement isn’t something that was a part of the country’s governance for the first 200 or so years of its existence.