The problems you specify here are not unique to Overwatch but are common issues across all major online team-competitive titles. Yes it is hard to identify and implement measures to prevent disruptive players such as those who would throw games to keep their rank low or those who want to use third-party software to cheat. This is because players who look to disrupt games try to find ways to work around rules and guidelines like the Blizzard In-Game Code of Conduct. Cheat developers work around known detection methods and improve their software. Blizzard has a comprehensive hacks and risks team that works to constantly fight those efforts. If you see these activities in other players, report them. Note, reporting players because they are on a new account regardless of how good they are is not against the rules.
I do know Blizzard sees the feedback regarding disruptive players in Overwatch and they have recently said there will be new features and steps of action to help prevent and correct such behavior. I understand your frustration, but I do ask that if you see anything that breaks the in-game code of conduct, please report it.