I'm slightly confused. If we're talking about competitive, you would want your MMR to actively reflect your skill level. If you did well, you would earn more credit for your performance. Why should someone who hasn't contributed as much whether it's factoring KDA or objectives like plants and defuses get the same elo gain as someone whose numbers show that they were one of the players that performed really well?
Maybe a bad example but does someone who averaged 100 combat score deserve the same elo gain as someone who had 300?