It's 2019 and this guy only complains now?
The reason why win rate is weighed much less than damage is because of how common it is to be absolutely useless in any given match and still get carried to victory by good players doing all the heavy lifting. Your one single shot of 200 damage in a Maus and death within 3 minutes of spawn should be and is correctly weighed significantly less than the STB pulling 6k damage out of its ass and carrying your dead weight for a win. Likewise, if that STB was in a platoon with two other good players they will probably still win and likely have an easier time for that matter, but they might only be doing 4k damage each but still carry each other.
The opposite is also true, in that it is also very common for bad players lose games that are otherwise very winnable, but because they are absolutely useless they manage to make everybody on their team lose instead. A platoon of 3x SConqs should be able to facetank and kill everything in front of them, but what if they all die at the 4 minute mark doing only 2k damage combined because they drove ass first into the enemy? Suddenly their whole team lose considerable chunks of health and firepower, and in the case that they lose the three retarded SConqs are to be blamed. If they somehow pull a win out of their asses, that's great but the SConqs were still inconsequential because they did absolutely nothing to contribute to the win. It is also right that a 140 that pulled 4k damage before losing (or winning) should be seen as having performed better than the SConqs.
This is why damage dealt is a much more useful metric in measuring the performance of a player than win rate.
Shitters have always been useless for one reason or another. Before performance metrics they camped to stay alive and avoid repair bills, or wanted to defend arty, or wanted to defend cap before anyone has driven past half the map. Shitters are shitters and will do everything in their power to play as shit as possible, that's why they are called shitters.
You want to win more? Git gud and carry harder.