Willie Pep. Billy Conn. Lol at Usyk. Being able to hit hard enough to deter 240-275 lb men from attacking you isn't being a pillow fist.
Midget Wolgast 17 KO wins in 216 fights. Jack Britton 30 KO wins in 344 fights. Not necessarily my favourites (though I do have a soft spot for Wolgast), but certainly ATGs with very low KO percentages.
Didn't even think of him as a pillow fist until I read his name in the thread and thought, fair. Got to be Usyk. GOAT quality low KO artist.
Marty Jakobowski. Bet nobody else mentions him, but he was the king of Pillow Gloves and fought a zillion times through the Midwest
He'd be hard pressed to be above Jimmy Young. Young's resume and close decision losses speak for themselves.