Remove any in-game display of career/seasonal KDA. Only KDA that should matter is at the end of the match. Leave it to the 3rd party sites to track so only true tryhards even care about it. Remove the flex and you might have less players leaving matches.
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The main biggest reason for quitting games midway isn't kd/a but it's irl stuff and distaste to maps and/or playing disliking being killed by certain weapons. Those are the biggest reasons people leave games. For me it's maps if I get onto one of those new 4 maps this season I'll just leave before the game even starts.