ut it does give the serious impression someone doesn't trust either Hawkeye or Renner to carry audience interest enough on their own.

I think Marvel/Disney didn't have much of an option on this case: the MCU version of Hawkeye has never been that much interesting and while Renner isn't a bad actor, there's just too much controversy around him. Bringing in two female characters who actually make sense to be there is a good move.