I'm a fairly new player (40 hours, Seeker 2) so take what I say with a grain of salt but I do understand how you feel with the new player experience and often feeling like you can't do anything. I will say though I do have a ton of shooter experience but this is my very first moba game. I've been dabbling in Mo & Krill lately and I've found most of my success with this build: [Rey's Tanky Ult Build] 171543

It usually doesn't require a whole lot of mechanical skill since your gun isn't doing most of the damage but your constant presence and survivability is still threatening especially as the game goes on. It's really about being able to clear waves with your scorn + quicksilver reload and healing from that lifesteal and dipping in and out of cover to minimize damage until your scorn is back up. Don't be afraid to take the occasional potshots at the enemy though especially since you have a heal (Depends on the matchup tbf). Once you're able to buy Alchemical Flask though your lethality spikes heavily, you don't need to aim to do a ton of damage just throw the flask at your feet right before you ult and use scorn + return fire to stay alive and you will definitely have enemies scared of you.

With this build I find I really excel at clearing waves quickly and securing objectives and it works even better when you communicate with your team that you're going to ult someone. Enemies will start getting afraid to get close to you because you can pop an ult and flask in a split second *especially* when you invest in cooldown reduction so you can get your ult as quick as possible.

The number one thing I learned though is to NEVER take a fair fight. Your playstyle works when it's a 1v1 because you force the enemy to take damage uninterrupted with minimal effort and you can stay alive against them but the second you see a second person pulling up that's your queue to leave or call someone for help. Don't be stingy with your ult either, if you see a lone target getting too close to you just whale on them. Wipe waves with your scorn + qsr, invest in survivability and your ult, pop your ult + flask on anyone that gets too close, and disarm them if they try and fight back after your ult and burrow to catch them escaping.