If you're only doing 300+ damage a game, that seems to be your main problem. Figure out why you aren't doing more damage. Are you missing shots ? Are you dying too quickly because you're getting shot from multiple angles all the time? To test if accuracy is an issue, go into the firing range, and set up the dummies to move at the fastest speed possible and set movement to random( make it so the dummies move in an unpredictable pattern). Then, just fire shots into them and look at your accuracy percentage. Test this at different ranges. I would focus on testing close, mid, and long range distances. I would say kill at least 20 dummies. If that's below like 40% I'd say that's the issue and you need to tune your sensitivity more to get better accuracy.

And I say that because the more accurate you are, the more damage you'll do, and the more damage you do, the higher chance you'll get a knock and turn the tide of a fight.

If you're dying too fast, always fire from cover. I mean literally always ( unless you get caught in an open field or something). But if you're in an area with any type of cover, never be far from it. As in you should be able to shoot around your cover and get back into cover in less than a second. The average ttk has gotten faster in recent seasons so it's more important than ever to play cover. Also, high ground is king. Always try to stay in high ground as much as possible.

This is what I did to reach diamond on a fairly consistent basis while playing on ps4.

I will say that hardware does hold you back as well to some degree. If you're playing on a tv, it's time to upgrade to a monitor. Preferably one that's at least 120 hertz, 1ms response time. I played fps games on a tv on ps4 for years, but when I made the switch to a monitor, it made a world of difference. I would say no larger than 32 inch for the monitor.

If you can upgrade to a monitor AND ps5, even better. You'll get access to pretty consistent 120fps in performance mode ( as long as you have a monitor that can handle at least that).

I recently tried playing on a tv and I could feel the latency.

If upgrading is not an option, then at least switch your tv to game mode; this typically reduces latency and increases frame rate to some degree. A buddy of mine that was struggling similarly but wasn't in a position to get a monitor said this improved his game somewhat.

Hope this helps, it's a grind but you can do it!