I find these kind of matchups almost impossible to analyse. On the one hand, you've got a fighter whose career spanned 26 years from 1904 and 1930 and had over 300 fights. The sport changed so much during this period, particularly from 1920 onwards when Britton was starting to come to the end of his best years. Britton is a lock for a top 10 spot all time at welterweight. DeMarco, a fighter from the late 40s to the early 60s, will never be considered a greater fighter than Britton but how his style of fighting from the 50s measures up with an old-timer like Britton is really hard to say.
Yea,your right, not easy to appraise, on balance given that JB is one of the greats ( sort of ) not withstanding you don't, see him in a lot of peoples top ten do you ? feel he will have to much guile and ring craft to off set De Marcos aggression and potent left hook, so prob JB on a wide points win. keep well.