For many people, top fragging is really important and a great morale booster, while bottom fragging makes you feel bad. The scoreboard should be changed so that its easier for non-duelists to frag higher. I'm not saying that only duelists can frag high, but you can't deny that they are built to get kills, while other agents are built to assist.
Assists should influence the scoreboard much more. I have seen bottom fraggers with 4-10-15 when there are people above them at 6-12-3. clearly the person with 15 assists should be rated higher.
Other things such as using util to flash/damage enemies or smoking off areas (could be calculated by detecting whether an enemy has to walk through a smoke then gets killed after exiting or if they walk through where the smoke was just was after it disappeared) should contribute to a score that actually determines where people frag. For example, a kill gets you 100 score, assist 50 and death -50, while flashing enemies gives 20 per enemy flashed and -20 per teammate flashed etc. This would allow controllers, initiators or sentinels to frag higher if they are supporting with information instead of kills.
Getting information should also give assists/score. If someone was revealed by a sova dart/cypher cam/fade haunt and they get killed, that should count as an assist (correct me if it does already). Spotting enemies should give small amounts of score so that people that are just getting info can frag higher.
Finally, (and this isn't final so don't flame me about it) is giving score (not out of your own score) to people who do well. If your killjoy completely holds a site by themselves and buy your team enough time to get there, you can give them some score for doing a good job. I know this could be used to get one person tons of score so the amount you can give is a small amount per round, with maybe a bonus to the player if multiple people give them score.
Note: This is all a suggestion, don't take it to seriously.