I get having an item to speed grinding for people that just want to get S ranks faster or whatever, but when there's a leaderboard for scores accumulated during a season and it's the only place to get RSR continously (which is still ridiculous btw), this is the literal definition of pay to win. What's worse, with how easy the ranks have gotten in the past update and how the daily challenges take just four or five matches to complete, there is literally no reason to pay for the Boost unless you want to pay your way up the leaderboards. There's no other real use for it.
Either make the extra score not get added to the leaderboard or just call things by their name, but this is blatant pay to win.