Valve do listen to the competitive community. In 2014, after months of being ridiculously OP, valve had the final straw with the cz75 in csgo after Dreamhack Winter 2014 (the major) after it was 4th-used weapon at the event, with nearly as many kills as the AWP. https://www.hltv.org/stats?event=1553 They nerfed the fuck out of it 2 weeks after the event ended. They did something similar with the tec-9 two weeks after it was shown to be OP at ESL One Katowice.
Note that these weapons had been OP for months but the final straw was them being shown to be utterly game-breaking at the highest level. They then tried to introduce the r8 revolver but after being shown to be completely and utterly game-breaking, it was banned by tournaments and valve quickly nerfed the fuck out of it. Since then, valve haven't added any game-breaking weapons to the game.
Want to know the difference between the r8 being banned by CSGO tournaments and the 6s whitelist? CSGO tournaments use almost exactly the same rules and shit as Valve matchmaking.