Was June Allyson doing Lucille or Sue? I don't recall Keeler sang that much in the show, as even when she does "Take a Little One Step" on the OCR, the arrangement just can't wait to get the boys in to supplement and sing along with her musical phrases. It's kind of funny how obviously they want to have her sing --- just a little-- by herself. Allyson kind of underwhelmed in some of her movie singing too with her throaty voice, but apparently in the 1940s and into the 1950s she was very popular as a non-glamorous girl-next-door type. I'd say her movie persona has dated more than others. She's ok in "Good News" and her dancing in "Thou Swell" in "Till the Clouds Go By", but otherwise many others more shine more brightly than she when looking back.
Years ago, I once asked a knowledgeable friend what was the big deal about Ruby Keeler -- she didn't sing or act that well in her old films, and she looked at her feet sometimes when she danced and wasn't the best dancer by a long shot even when she didn't look down. She did have a certain charm about her though, as if she could do it, almost anyone could (overlooking that she married Al Jolson who helped her). My friend said it was more the fact that she appeared in some great films with incredible musical numbers and visual effects and that she was part of it that the whole nostalgia and fondness for her place in film history came about.