Yes, Brink could use many things. Many more choices, more maps, more of everything, more kits.
But one thing that is missing, is loyalty. When I decided I was going to buy this game, I wanted to BE a security agent, not a resistance low life. And I don’t want to play as a resistance agent either. It makes the game worse for me, because as a middle class American who has invested a lot in many things, I don’t want to give them to others. So, this could cause loyalty so that we could eventually feel like a faction is OURS. This would even add to the game play’s story without any voice acting.
EXAMPLE OF IT BEING DONE CORRECTLY-
MAG. This game does it excellently. Any time there was a youtube video, people would post thing’s like SVER forever. Or Slaying Valor Eradicating Raven. Or Raven’s are the smartest. Why? Because we felt the faction was personal. That was the only faction we played for, and we KNEW our teammates well. We felt like we were fighting for our faction- not ourselves. They didn’t need it but they even included a bonus system for the factions that were winning a lot. This added to the story through mechanics, making the game MUCH better than it really was. No one didn’t use teamwork because no one wanted the loss to be their fault. (Happened to me. We lost a contract because I got greedy and didn’t repair the AA battery. Jesus)
HOW TO DO IT ON BRINK
First, Let us pick a faction at the start (You already did) and then let us play as that faction only in multiplayer, unless needed for balance reason. And the reward if your faction does well? The easy way to do it is keep track of the wins (YOU ALREADY DO) and simply give the winning side the advantage in the Ark. Example- if Resistance does really well, make the storyline seem like the resistance is winning. Make it so Resistance attacks the homes of the security. Revisit Security tower to capture it forever. Or something. Maybe even give the resistance a health buff. Maybe even kill the captain of the security. You don’t need cutscenes though. That cuts down on production times.
(If a faction wins three times though, that will signal a need for balance.)


(I love my Resistance SuperMedic, with his doctor mask, ripped beater and sweatpants, but it’s technically a Security character)