It's normal. Just bad games and good games. I frequently queue solo and top the chart nearly all the time. However, i can't really win the game by myself even with all the numbers I pulled. One thing I can suggest is to bind target's target and target nearby friendly for a fast switch guard. My average with parakeet is about 250k damage/50k protection 10-12 medals.
PS: I switch guard constantly and fast depending on who's getting attacked, their HP, and number of enemies. There's no point of guarding someone not taking damage even if it's your healbot. Also, cancel your guard when you and your guarded target get bombarded by aoe.