There needs to be a "match me only with people in my league" option
I.e. if you're silver, you will only get matched with and against other silver players. If you're plat, you will only get matched with and against other plats. Keyword here is "option". Make it a clickable button somewhere for normal games and TB games. This way people who don't like longer queue times won't be forced into them while people who don't care won't have to face people far beyond their skill level. While this won't change the fact that smurfs will still be a thing, it might at least curb the over-zealous plats/diamonds vs. silver/gold games that are rampant in normals. Furthermore, if it's made an option, there is literally no downside to installing it: people can choose to take part or not, and neither side is any the worse for it.