The claim that the Founding Fathers had no conception of the filibuster is not true. If you read Robert Caro's "Master of the Senate" (part three in his four volume biography of Lyndon Johnson), there is a passage where he talks about Founding Father George Washington's conviction that Congress should consist of two houses, the House of Representatives and the Senate. Washington explains that one chamber should act as a saucer does to coffee, to "cool" It. (If this doesn't make sense, you need to understand that saucers were invented so you can pour hot coffee into it, allowing it to cool, before you poured it back into the cup, not as cup holders or coasters, as they sre comminly used today).
Moreover, the Founding Father's understood both checks and balances, as well as the concept of "majority rule with minority rights." Both are encoded into our Constitution.
The filibuster keeps one party from ramming its agenda through. It also prevents the subsequently-elected party from undoing that agenda, by ramming its agenda through. It's an important part of American democracy.