I play Fragger, Sawbonez and Proxy as my “mains” with Vassili as a counter-pick on some maps. My score is pretty competitive between the classes. The highest score on a side I’ve ever gotten was with Sawbonez followed by Vassili despite typically dropping 35-45 kills a side when I play Fragger. You have to play the class to their fullest to get a high XP score. You do not suicide rush objectives to try and plant/defuse as proxy while also putting down a mine here or there. You actually have to kill people, flank them, put down smart mines and also go for the objectives. If you do that your score will always be high. If you go 6-20 on a side suiciding you’re not going to do well in comparison.
I’m sure the scoring system isn’t perfect but it’s definitely better than most other games I’ve played in the past where there were always extreme standouts. Good players who play their classes well will get pretty high scores.