I think you might enjoy the game better if you ignore the FOTM Revenants and farm equipment the traditional way.
Possibly, but since this is a Diablo-like you still want that dopamine rush you get for finging new loot and nothing compares to what the remnants drop.
And yes, while it's true that remnants have other weapons the Odachi is just much more common and chances are the highest level weapon you'll find after sweeping a mission is going to be an Odachi you got off a remnant.
BTW, i genuinely had no idea this weapon was so popular. Even though this game is very different from Sekiro the latter was still in my mind when i started playing this so i consciously decided to avoid straight swords and decided to pick an heavy weapon instead, just to be different. In the process, i accidentally ended up doing what everybody else is doing, heh.
At any rate, i think i'll switch up anyway.