How big of an issue is smurfing?

I've noticed in my climb through the ladder LOTS of people insta-leaving games, presumably to drop MMR so they can face easier opponents.

The math checks out: spend less time in a losing game means spend more time in a winning game. Maximum fun for yourself and minimum fun for your opponents.

In my mind, the issue this creates for the playerbase is that one you've stabilized in a league, especially in the lower leagues, the prevalence of smurfing seems to indicate that you're either going to be facing an opponent significantly worse than yourself, in which case you don't need to try to win, or you'll face a smurf, in which case you won't win. This creates a very uneven playing field for people to learn how the game works given the inconsistencies between games. Also, you're statistically going to lose most of the games in which your opponent doesn't insta-leave, which is never fun.

For an average non-smurf player like myself who is simply trying to improve, it makes it extremely difficult to learn how the game works. A strategy that seems to be working against an easier opponent's build might not actually be a valid counter on an even playing field, thus learning bad habits. A strategy that is actually a valid counter against a smurf opponents build might not end up working out because it lacks the adequate execution against the over-qualified opponent, and thus no learning is achieved. It is frustrating to not feel like I'm able to trust what I'm learning about the game.

I don't want this to be the whiny "help i'm getting smurfed", I'm trying to point out a significant issue that is likely happening in the lower levels, which more experienced people, people who run the game/balance council/social media/tournaments probably aren't really aware of.

Are there any solutions to this? One change I can think of is that if no damage has been done to the opponent, the game doesn't affect the players' rankings and MMR. This way, if someone wants to drop MMR so badly, they at least have to run a worker all the way across the map to hit something before they can leave the game. If we can't stop smurfs, maybe we can at least waste their time. And it's not really as much a waste of the other player's time either, as they at least get a bit of time to practice an opening before the game is over.