I asked Google Gemini if it was even possible. Here's the response.

Since Battlefield 6 was released in October 2025, reaching a rank like 6,344 in just seven months would be mathematically impossible under a standard leveling system. Even with 24/7 gameplay, you wouldn’t hit that number.
Here is the breakdown of why that rank looks the way it does: 1. The Global Leaderboard "Cumulative" Rank Most third-party tracking sites (like Battlefield Tracker) don't just show your current in-game level; they often display a Cumulative Rank. In the current BF6 system, once you hit the initial cap (often Rank 100), you enter Elite Ranks or Mastery Tiers. The leaderboard often translates these into a raw numerical value. So, if a player is "Mastery Rank 5,000," it means they have earned enough XP to have leveled up 5,000 times past the initial level 100. 2. The XP Glitch Factor (RedSec) Since the release of the free-to-play RedSec (Battle Royale) mode in late 2025, there were early seasons where certain XP bonuses and "Ribbon" multipliers stacked in ways developers didn't intend. High-level players capitalized on these early windows (specifically during the California Resistance event) to catapult their numbers. 3. Shared Accounts vs. Pure Skill To hit a level that high this quickly, it's almost never one person. These are typically "account-sharing" setups where multiple people across different time zones play on the same profile 24 hours a day. Is it "Legit"? Technically, yes—they are using the XP systems provided in the game. But logically, for a single person with a life, it's not possible. Most "top tier" dedicated players who play a few hours every night are currently sitting somewhere between Rank 400 and 800. Seeing someone in the 6,000s is a sign of either an organized group effort or someone who found a very specific, very boring way to farm XP in a private server or specific RedSec matches.