By Jamie Spencer The biggest thing that held Manchester United back last season is the same thing that has been their biggest improvement so far this season: squad depth. United cruised to a 4-0 win over Brighton on Sunday to win their first three games of a WSL season for the first time. They have scored 10 times over those three wins, are yet to concede, and have scored seven times in the first halves of their two home games alone. It could have been a challenge for United to take Brighton apart in the manner they did to Reading last month. The notable absentee from the squad was Alessia Rus…