Can we talk for a minute about normals matchmaking?

Recently, there has been a trend in matchmaking in normals to match me, a s5 player, and my friend/duo, a lvl 25 unranked novice (no insult bro) against teams that have 2 plats, 2 golds, and an unranked or something else ridiculous like that. Can somebody explain to me how matchmaking in normals works/is supposed to work and why this happens? Because it honestly makes games pretty unfunny and unwinnable.