Rank and experience (xp) in TW (and player skill)
First, let us agree that rank is different from experience.
Rank is an agreement between players for who is in charge, so a ranking system could be agreed by the team for their own purposes. There is no need for a mechanism to apply rank to characters in the game other than for decoration. For example, to gain medals or other recognition.
XP, if we follow Aniallator's logic, should not accumulate because each game is separate. I agree so long as the game is not part of a campaign.
XP has a place where a character (that belongs to a player) participates in a campaign of several battles. Success in a campaign game therefore earns XP which is spent by the player to improve his character's skills. For example, 3 XP earned in a game to spend on fitness, weapon handling, demolitions, radio, driving, heavy weapons. (The list depends on what is implemented.) The gain in skills would represent how a recruit improves by experience in combat. If the character is killed then all is lost.
How XP is earned is another topic.
Perhaps you would agree that player skill is not something to program or allow for. The realism that is part of the game design remains within its limits without changing over time. Hence, being good at the game is a personal goal and why you would be part of a team.