Actually T500 is just an easily understandable illustration of a greater phenomenon. No one is preventing anyone else from achieving T500 either. If you want T500 just climb higher than the guy who has 4 spots. To be T500 all you have to do is win the games for your SR to be higher than one of those 500 accounts. Smurfing doesn’t gatekeep you out of it because you don’t stop winning SR for a win or losing it for a loss. You can just win more games if you want to climb that leaderboard. Starting to sound familiar?
Also T500 is just a percentile rank like any of the other rank for the most part. It’s limit is more finely described than bell curve distribution, but it’s the same principal. For example let’s say there’s 3000 GM in a region. We know about 1% of comp players are GM so that means T500 represents 0.17% of the players. I don’t know the real number because idk how many GMs there are, but there will obviously be a percentile at which T500 starts so I’m just going with an easy to work with number.
If you want to get T500 you just need to win the games to hit that top 0.17 percentile. No one is preventing you from winning those games. But I think we can both agree less people will be in the top 0.17 percentile if the same say T10 player has like 4-5 accounts in T500. That said just like you argued this person hasn’t prevented anyone from hitting T500, they can still win games and increase their SR to this range. But undeniably as more duplicate accounts occupy the top 0.17 percentile then less distinct individuals will be represented in T500.
This phenomenon doesn’t suddenly change for ranks below T500. If half of active GM accounts are smurfs then the bell curve - which results in the top 1% of players being GM - will only be half unique individuals. Jumping back to the 3000 example if 1500 of those accounts are smurfs then that’s 1500 less unique individuals who will achieve GM. Just like in the T500 situation you can say ‘but just win more games, it’s not like your SR won’t increase if you do that’. But nonetheless half as many unique individuals are gonna reach GM in this hypothetical because the system is belled towards a particular distribution and many accounts above that percentile are duplicates. T500 just offers an obvious example of a percentile being harder to achieve if there’s duplicate accounts occupying it.
All this isn’t to say ‘waaa I should be gm’. I think I’m at the correct rank. But this is just to illustrate why smurfing inherently and necessarily affects the number of unique individuals at any particular rank.