Casting ordinary-looking people in lead roles certainly makes things more believable. I always feel sorry for what they call ‘Character Actors’. Character Actor = good actor that everyone recognises and likes but who almost never get to play the lead e.g Emma Chambers, Phil Davis, Miriam Margoles, Toby Jones, Penelope Wilton, Danny Webb, Frances de la Tour, Michael Kitchen, Andrew Scott . . .
It pays the bills, but it must surely be a bit soul-destroying.