Official site:
Soon, players will notice changes to matchmaking — specifically, you’ll only be seeing vehicles one tier above or below your vehicle’s tier. This change is being implemented in the name of better team balance, but keep in mind that it’s only a trial run for the NA server, other servers will not be affected.
Based on matchmaking performance and player feedback, it may be brought back as a permanent feature, but right now we’re just testing the waters. The duration of this trial run is still to be determined, but look for it between Update 2.5 and Update 2.6.
