I'm probably going to make a lot of suggestions that people have already said, but in all honesty, I'm too lazy to sift through all of that so I apologize in advance <3

INCREASING PLAYERBASE

• Advertisement. In all honesty I never heard about this game until it became free to play. Even then I completely forgot about it due to the lack of game news covering it. I only recently tried out the game because I happened to remember about it while scouring for games. (This might also fix the issues with matchmaking)

CHARACTERS

• I think characters should not be locked by levels. It's not difficult to unlock them (personally) by reaching the level, but telling a player to reach this level to unlock a specific character is a bit discouraging since (at least what I assume is the concept) characters should be balanced, but have different playstyles; getting a higher level to unlock the character doesn't mean that the character is anymore OP than someone like Lycus. However, I think it would be interesting to have players unlock characters by completing their respective missions. I.e. unlocking Schneider when you defeat him.
• When players unlock a new character, give them the option to play a tutorial mode that teaches them how to use the character (I'm looking at you Harec).
• I'm all up for players having to pay Mercury points for premium costumes, but show some love for the freemium players. Maybe release specific costume options for freemium players that require either/both gold or/and faction points to get.
• MORE EMOTES

CARDS

• The card system is essentially a lootbox system, which a lot of people aren't a fan of. Also the fact that you can only keep 8 cards total limits playstyle and diversity. Why not make the card system more of a collector/gacha style. Sure it's still lootbox-ish, but why not give the player an option to be refunded either 400 gold or 400 faction points for each duplicate they get. That way they won't be as upset by it.

CAMPAIGNS

• Make campaigns for why certain enemies defect to the raiders. For example, why would Aneska become a Raider? Maybe because the leader of the faction deems her useless, and wants her dead, so she flees to the Raiders, wanting revenge.
• After playing the same stages over and over again, it gets tiring to play the game (at least for me). Maybe make different maps for the same type of stage. Look at Warframe for example, same exact mission, but gameplay feels different and fresh because the tile set keeps changing.
• Why are stages locked by levels? I don't think it's fair for a player to have to be level 90 to unlock a stage when a level 10 can unlock it just the same if they decide to choose that campaign first. Maybe require faction points to unlock the stage instead

GAMEPLAY

• A chat system during gameplay. If not that then a more complex signaling/command system besides the 4 that we have. i.e. "Retreat" "Wait here" "Group Up" "Enemy here"
• Antagonists can sacrifice a non-elite mob for extra bullets.

Miscellaneous

• Why does lore require faction points? Other than getting more info about the world, you don't get much out of it. Why not reward players for completing a lore, for example a title to equip to their name that shows up in game. Maybe it gives bonus stats! Idk, think about it.
• I don't understand the importance of Ranks as rewards? Do they do something? Doesn't look like it, at least for me. Maybe increase the number of special rewards you can see on the map the higher your rank?
• I just don't enjoy the rotation based rewards. The possible rewards to gain are very few, especially for players like me who play for hours. With the 24/12hr rewards as they are now, I can probably get them all in 1 hour of gameplay. you could probably do a system where if you complete all the rewards available, they reset. Or some additional reward challenges such as, "Kill this many elites" "Win without losing more than a whole set of lives."
• Sprays like those in Paladins/Warframe
• Marking points like that in Warframe
• New Stage idea: Don't get spotted by an enemy
• New Stage idea: Outrun the flood of enemies
• New Stage idea: Fight an army of our clones
• New Mode idea: Beat every major boss in a row (with increasing difficulty)
• New Mode idea: 2v2v2v2 (or 3v3) Last team standing in a hoard of enemies
• Please don't make a guild war thing. It FORCES guilds to be active/participate in stuff (or makes it very alluring)
• Increasing Guild Rank increases number of members allowed (adjustable)
• Use faction points to purchase different backgrounds on home screen
• Daily Login (reluctant about this idea cause I usually don't like it, but think about it)
• Cosmetic rewards for specific levels

MMR needs a rework. I just played as a lvl72 (MMR 32%) Antagonist against a team of completely new players (the highest being lvl 9, the second highest being lvl 2, and the other two being lvl 1). Needless to say the match was over in 5 min. How can anyone expect these types of player to "Get Good," if they get curb stomped by high level Antags with what I assume is a lvl 9 mentor?

On another note, I do think the idea of a mentor system is great, but carrying an entire team of new players is not fun gameplay. The other day, I lost ~10% MMR (was originally MMR 42%) because I was constantly teamed up with 3 other players who had little understanding of the mechanics of the game. In EVERY match (literally), I'd have at least 2 members disconnect from what I assume is pure frustration because they were constantly dying every 30 seconds. I think the best way to correct this would be to have at least 2 high level players in a mentor match, because without any decent way to communicate to these new players, they will just keep dying due to poor understanding of the gameplay mechanics/objectives/tactics, and the gameplay will just be unnaturally difficult.

Additional notes; for every new player in a match, an additional 20% exp should be given to the mentor, otherwise it's not rewarding to play a 30 to 40 min match with a team of new players to only get 20% extra exp.

Extra notes; I think new players should be considered NEW players for mentor matches until they reach level 15. No offense to any of these players, but a lot of them don't seem to understand any of the game mechanics until around lvl 20. I've seen many players at level 15 die from very basic things, such as charging straight into a mob without any backup, or staying outside of sight from the beholder (not dying once but repeatedly dying from the same thing every 30 seconds). These players haven't gotten accustomed to the playstyle necessary to become a mentor themselves.