How Top 500 actually works
Top 500 is not a rank you hold like a tier — it is a leaderboard, and there is a separate one for each role and for each region and platform. That means the Top 500 for Tank in your region is its own list, distinct from Damage or Support and from other regions, so a boost targets one specific leaderboard rather than a single global spot. You also have to have played enough ranked games in the season to be eligible for placement on it, and the boards update on a snapshot rather than the instant you win, so a qualifying rank shows up when the leaderboard next refreshes.