At risk of overgeneralizing, the problem with creating tiered rewards for PvP, especially for NA servers, is that it creates incentives for cheating/collusion. Unfortunately, anyone who has played PvP MMOs (think Lineage 2, Black Desert, Archeage), knows that the NA playerbase tends to look for exploits/ways to game the system when it comes to performance-based PvP (ex: match-fixing, sync queuing, etc.). Granted, it's much harder to do with Frontlines because of the sheer quantity of players (you would have to be super coordinated across multiple servers to meaningfully engage in matchfixing), but I wouldn't put it past the player base to do something underhanded if the incentives are there.
