I never said there wasn't smurfs, but I also think it's unfair to not give credit to players who have a good game. I say this because I've seen posts claiming that every single game has a smurf, when realistically that's impossible.
Even using your past season triangle example, we have a group of devs that constantly have been radiant and play 3-4 hours every single day, that have been playing more unrated then ranked. Some of those devs don't have an act rank triangle this act.
Also, most smurfs will struggle to stay at low ranks. It's very hard to have an account maintain a rank, while also smurfing on low ranking players. It's kind of a complete counter to how ranked works, because if you are truly smurfing you would increase your MMR and no longer be smurfing. We can detect this very quickly, for example TenZ getting radiant MMR in less then 20 matches. It would happen for anyone below radiant in even shorter time(the extreme high ranks, like radiant, take the longest to shift MMR into). This is even harder in our system because we don't put barriers on ranked/MMR - and match you based on your MMR. On top of us having a performance MMR which can tell if you are performing outside of your current matches.
So then if players are going to be pushed to a higher MMR, due to smurfing and having "insane" games against low ranking players, they would have to make an another account. Which again people will do, but becomes less frequent because at some point making multiple smurfs takes a lot of time not playing the game(or money to buy a botted account that will just get banned eventually). It's just another barrier that reduces how many people smurf.
I'm just being completely open, and honest, in saying that when we investigate smurfing it's not as big of an issue as people think it is. It comes down to wanting to find a reason why you may have lost a game. Again, I'm not denying that you will encounter smurfs - it's just unrealistic to think it's as often as the community believes it is.
I used plat as the example, because that was what this player refrenced when talking about smurfing. But even if you tried to argue about smurfing in silver and below, that's 50% of all players. Not only would that require a sizeable chunk of players, ranked gold and above, to smurf. That would also take players out of the higher ranks, and you would see issues like increased match making time, worse match making due to skill gaps in MMR(due to missing players), etc. Because you would need those players to constantly be smurfing, and you would need to maintain a large % of those high ranking players constantly smurfing to maintain even a 1 in 5 games smurf occurance.
Like I said, every decision we make also takes into account how it may help reduce smurfing. And even if I say "Smurfing isn't as big of a problem as it is" I understand there will be edge cases, or you can just straight up not believe me. Because when you are in game, encountering these issues(or feel like you are), it's counter to what I'm saying. That's why, we focus on design decisions to reduce smurfing as a whole. We will always try to help reduce the need to smurf, or reduce the ability for players to smurf.