Weight is major and to state otherwise is deluding yourself.

Mary, your assumption that the old sails better suit the old boat also has issues but lets keep it to one argument at a time.

A couple of case studies.

2 boats get perfect starts on a perfectly laid line. Assuming both boats are travelling at the same slowish speed when they cross the line the boat that gets to full speed first will have a definite advantage. If its the windward boat it will overhaul and then gas the leeward. If its the leeward boat its foils will generate more lift sooner (due to its increased speed) and it will pull ahead and then lee bow the windward boat. Either way the light boat wins.

You go around the top mark a boat length apart. If the lead boat is lighter it will accelerate away and the aft boat won't get a chance to attack. If the aft boat is lighter it will make up ground on the maneuver and be sitting in an attacking position when the two boats reach full speed.

If you do some quick back of an envelope calcs you'll see that without even considering the added drag while at speed at boat+crew that is 10% heavier will loose about 1/2 a boat length on every maneuver.