My NA account is 3.5K MMR, which isn’t platinum. But as I didn’t hit the 25 games, and didn’t feel the need to, it’s still in provisional MMR.
My EU account is currently between 3.1 and 3.2K, but for some reason I am being matched with 80% of diamonds. I recently tend to win a lot of them btw. And occasionally, even some smurfs, though they ruined my ratio lately.
What you’ve described here are non freelosing smurfs, who are about one fourth of the smurfs. A majority of smurfs do freelose games either regularly or in streaks in order to avoid getting to a MMR where they’d find a suitable challenge. So they can stay indefinitely in diamond, platinum, gold, even bronze 3 if they’re willing to.
And that is why gold and bronze3 are probably the leagues where there are the most smurfs. 
Back at the guy who complains about smurfs without ever understanding they were freelosing.
If you want facts, there is a 100 posts thread linked just above which includes detailed randomized surveys about smurfs in 3+ leagues. Those surveys are way more accurate than your lifted finger personal estimates could ever be. If you just want to keep crying though, be my guest and just remain a ranting ignorant. 