The OP is right.
He didnt give his idea any thought.
Leagues work for a single entity. That can be a simgle person or it can be a team such as a footbal team, or a clan. It would not work for players in random battles because they are not playing as individuals, nor are they playing as part of a single team. They get switched into a different team with each new battle.
Leagues in WoT would be like taking the whole of the Premier League players and creating a pool of players that are then randomly divided into 20 teams for that weekends fixtures. And the following week, they would all be mixed up again. At the end of the season, who has won the league? Not the team, because there hasnt been a constant team. So it must be down to individual players, whose stats are going to be based on what? Number of wins? Points earned for number of kills? Or amount of damage done or blocked? or vehicles spotted? What figures would it be fair to apply in order to give a true reflection of a players rating based upon the different tanks a player might choose for their battles? What about number of battles played?
Because there is still going to battles that are determined by the type of vehicles, combined with the map, combined with the players own skills in their vehicle and its suitability for a particular map.
And leagues implies a relegation and promotion system, so the stats system has to be 100% watertight, otherwise there are going to be complaints about players manipulating their stats unfairly etc. Not to mention the complaints from players relegated because of the failure of their team etc.
A league system is theoretically possible, but it would need a lot of planning, a lot of coding, could potentially mean a lot of waiting for battles, and my guess is, it might please some, but it wont please all players.