Weapon Master is awful. Honestly if a player had a cool character concept and they wanted to use a weapon that their class didn't allow, I would just give it to them.
Every time I see these threads pop up, it affirms my belief that the feat system needs to be throw out and rebuilt. Every feat needs to be chopped in half. Balancing the current level of "power" that each feat needs to have has clearly proven too difficult. The devs backed themselves into a corner.
Make feats less powerful but grant more of them. I know the devs were resistant to too much choice but as it stands now, there is hardly any choice because the bulk of the feats are useless compared to a minority that are clearly superior.