I have thought of the filibuster as being something somewhat outside of the constitution. My suspicion is that it originally came about as something to preserve comity in the senate, in the sense that if the minority found something to be truly a threat to their most basic interests, they had a last resort available.
The republicans under McConnell have so abused the filibuster as to make it meaningless for that purpose, by destroying the basic level of respect and trust required for “comity” to exist. Very short-sighted and foolhardy thing to do, to my mind.