You surely can´t based who wins in a fantasy fight on how others rated them as welterweights? Walker was powerful as well but Walcott was in a different league, he was a freak like Langford, Fitzsimmons, Foster or Jackson. I don´t think there was a ww who punched harder including Robinson and Hearns.
I said that because I need to know more about Walcott, I was referring to how guys like Fleisher and co. I think Walcott edges him, I know he was short but as far as I know he had a great reach for his height.
The hardest punching WW I've seen is Tony DeMarco, I imagine that Walcott was at least as hard a puncher as Tony, if not more. But Walker had a hell of a chin.