Frontlines is a purely casual game mode. The jobs were not balanced with frontlines in mind. All but one of the game modes have elements of randomness in them that does not support fair competitive play. A 1v1v1 type of format also lends itself to unfair competitive play because you inevitably run into scenarios where one team does not play optimally and inadvertently helps another team (not necessarily intentionally either). So in short ALL frontlines is casual play just some people take wins/losses more seriously.

You probably could have guessed that I don't check my frontline standing very often as I don't see it as any kind of reflection of skill or achievement. It is fun though and I love the option to level up whatever I want by having some mindless fun