So for all my team ranked matches, my team has been completely wiped. I've maybe one 1 match. Does this mean I'm just stuck with crap teams combos?

The funny thing is, many of the ranked matches are just plagued by bad (fake?) players from 3rd world countries that dc often but not enough to leave the game. Just feel bummed about it...

The only way to win at Dota is to not play.

The best way to improve is to see what's wrong and understand why it's happening. Comb over your match history on Dotabuff and look for patterns - do you tend to lose more when playing certain heroes/roles, is there a problem with your team as a whole not capitalizing on your momentum and pushing when you have the opportunity, etc.

Personally I don't really put much stock in MMR, I've seen some 3-4k players with really really horrible game sense who flamed people for not buying the "right" items even though the situation clearly called for something else.

As someone that has played dota for nearly 10 years at this point, the best advice is to just play unranked until your super confident in your ability, and even after that maybe keep to unranked. The game is infinitely more fun if your not worried about your rank.

Pretty sure at that level it is not about hero choice. You could even make the argument that it is also less about knowing when to push/strategic flow/knowign when to do objectives.
But at that level I feel it is just fundamentals that need work. I.E. Last hitting, watching the map, good item decision, knowing the heroes.
Lot of those things aren't even good enough for people a lot higher.