wtf is up with MMR - can someone explain please

So apparently this system is meant to keep your win/loss rate @ 50% which it does.... kind ofBut how are you meant to climb when you get on a 3-5 game win streak and the system decides to put you up against teams that are 3-400 rating higher than you, until your on a 5 game loosing streak.I don't mind it when the teams are 100 rating above that's fine but when you get chucked into an arena and get stomped by a team who is literally 300+ rating higher than you is just absurd and that just happens over and over until you've spent 3 hours in Arena with literally no gains since MMR just decides that 50% win rate is more important that appropriate matching team ratings.