I have been playing dota2 for months now and I currently have a 50.36% win rate based on Dotabuff with 600+wins. Yet I still get matched with a bunch of seemingly beginner like players in my team. Case in point Matchmaking ID: 49613283 if you look at the replay im playing Sniper btw, my teammates dont have a clue as to what items to get, what skills to get, what to do in general. Its really annoying I hope they make a refined version of the matchmaking system....seriously.

i think , it rare case
me with only 290 win from 500 match never get matched with beginner like that

matchmaking is based from played match,level,win rate,party member etc
there such no way you can matched with ppl who played their first game


but in rare scenario it can be happen
example:
A new dota player start playing dota2 matchmaking using his friend/brother account (who have played 200 match)
then the new player will be matched with experienced player

or

party team who have big gap experience (party which consist of level 1 ppl and level 24 will have chance to destroy matchmaking)
the matchmaking will add at least "1 Beginner" to opposite team to mantain balance


there is no perfect formula for matchmaking against rare case like i mention above

The MM system is actually pretty awesome and I also know what u mean.....I watch Purges stream now and then and during one of them he explained that every player is where he must be in MM system....Think of it as hyperbole(or whatever is it called)....At the top of it where it is the thickest are most of the dota2 players, from beginners to medium/semi good players....As it goes down there are fewer player that are better than you and me,and at the bottom there are only pros(maybe)...watch this,maybe it will clarify better than me...
https://www.youtube.com/watch?v=BrOF55LAnqc&feature=player_detailpage&list=UUZsM8MOy0VC9blj_wBkbo-g#t=140s