Others have done a better job at saying this, but I’ll restate it for the sake of restating it as the first thing here.
-Progression System being tied only to Daily/Weekly Challenges is just plain terrible. Having a basic leveling system would do wonders. Example: Medals, Objectives, Kills, Sprees all earn you general EXP to level up a general level, with some of the exp going to the Battle Pass level, and having the Daily/Weekly Challenges be an extra source to earn EXP. With the current system it honestly feels like 343 is really wanting us to swipe our credit cards to buy the boosts.
-Player Customization. Player Customization right off the bat is really lackluster, and I feel I HAVE to buy from the store just to get any sort of customization options, or buy boosts for the Battlepass. With a general leveling system as I listed above for us to earn more Customization options would definitely go hand-n-hand! Sure we can earn through the Battlepass, but I really don’t want to buy the battlepass at all with the game in it’s current state. On another note, What happened to being able to swap between Covanent and Spartans? Lore aside, I always thought that was pretty cool! Why can’t I play as a regular Human Foot Soldier? Or, One of the Cast Members from Current/Past Story Modes? Why not a Grunt? A Brute? These added options will definitely open up the player experience with “unique” player characters they can call their own. One final thing, Colors/Dyes unlocked; or in general, should be open to all pieces of Armor, not just one thing. Really annoying and a big oversight.
-Matchmaking. I’ma keep it simple, do exactly what Splitgate does and allow us to toggle on/off what game modes we want to que up for. Example: “Ranked Matches- Toggle On: Slayer, Oddball, and Control.” It’s really as simple as that.
The only other thing is Weapons in general feel fairly weak imo, but then other times they’re really strong. Like, all the Energy weapons; specifically the Laser Rifle(can’t recall it’s exact name) feels very underpowered, and same goes for the Needler. Also, the Sliding mechanic feels very stiff, and delayed please 343 if you’re reading this, do something about that please. With that, this is just my critic on the game in it’s current state, Matchmaking and Level Progression I feel the majority of the community can definitely agree with, and have given feedback about. But, I wanted to give my own two cents on those matters and of course restate it for the sake of it stressing how important this being changed is important to everyone. Thank you for reading, and please feel free to give your own input/feedback in the comments below! I would love to hear what the rest of you think, whether it be on my criticism/feedback, or your own! 
Edit: I just wanted to make this clear. I really love how the game feels, and have enjoyed my time with it. But, with the game’s current system it’s not very satisfying for long. We need systems to keep players coming back, and feeling like they’re progressing in some sort of way.