I have always loved Ruby Keeler. In comparison to Powell, she has more energy and more spunk. Powell was much more polished, more of a professional dancer. It really is a reflection of the WB style vs MGM style. That street tough, blue-collar hoofer vs the elegant, grand final number with tons of sequins and shiny costumes.
I don’t think that the 42nd St number was the best choice for a comparison (especially not a colorized one). You can see that Keeler is performing true to the WB style in The finale of Footlight Parade, where her style perfectly matches James Cagney, another well known “hoofer”. Check it out.