Unfortunately leaver penalties whether they be the experience penalty for all modes or suspensions from Competitive Play must apply for all users even if they have disconnection. It takes a very large number of games to leave to trigger the -75% XP penalty, so really in this case, the penalty is applied because you are not taking the time to troubleshoot the issue.
Here are some resources to help troubleshoot your connection and information explaining Blizzard’s policy about disconnections and penalties.