Hi there, As mentioned, it was never against the rules to battle a guild-mate as long as the match is carried out legitimately.
To be more precise ->
Intentionally queuing against a user to aid yourself or another user in the form of Rating, PvP Coins, etc will be considered as Ranked Boosting and will be punished accordingly.
As long as the match was sincerely played, there shouldn't be a problem. Make sure to read How we enforce this rule to get a firm grasp on the same.
Although, I must mention, repeated outcomes against the same players may raise suspicion, if deemed as boosting, appropriate actions will be taken.
Regardless, I'd like to thank you for bringing this to our notice.
Best wishes,
Lekmino.