Écrou de fixation RP49835

I hate this nut with the fire of 1000 suns, So far I've put about 8 hours of labor into its removal and replacement. Have one of these stuck under my sink. Only 8 years old. Set screw head snapped off. Drilled it out. Can't rotate the nut now. None of the usual tools fit around this. Have tried penetrating oil, heat, banging with a hammer. Now some of the threads on the brass threading on the faucet base are beat up.

Why would you make a nut shaped like that? I am trying to replace my faucet and I can't get the old faucet because of the shape of the nut. Nothing works