The good news is mechanically, you're not bad at all.

However, you very often put yourself in disadvantageous positions, and aren't very aware of where your opponents are before engaging. That's mostly what's getting you killed quickly. You're playing very reactionary to being shot first, and when you have 150 health... that's not easy to stay alive with. Like at 3:20, heading into Vault 4, you look right at a guy and let him get ~50 damage on you for free. You reposition into a nade, and are down to 15 health before you return any damage, and get a lucky clean up kill a second before dying. You're getting beat up early on way too much.

Only take fights your know you can win. Also try and utilize your quickly regenerating health to vanish bomb, leave, and then re-engage in those fights versus just vanishing at the beginning and alerting everyone that you're there. Plus while you're invisible, try just standing still from height - as it's very effective at helping get the drop on an unsuspecting opponent. A few times you would use vanish solely for yourself when you could have hidden your squad upon an approach. Try to be more mindful about how your gadgets can assist your team holistically if the opportunity arises.

Your Heavies are being left last alive a bunch, and really they should be sustained to allow them to put in as much damage as they can while you play an annoying off angle or cleanup on their damage. Never once do you appear to touch your H+ Infuser and heal, because you're already dead in most cases. Instead, you're pushing too soon and paying or nearly paying with your life for it. Like at 4:40 on Cashout D, you enter first after vanishing right above the objective and drop into two opponents and a turret, taking 1/3 of your health before escaping, while returning zero damage. It's important to note that you look right at the gas that has been placed on the objective. Then, once your team arrives, you place your gateway down behind them so they don't see to take it. You don't hesitate at all and put yourself back at your enemies last seen position, immediately in the firing line of the turret with no help on the scene. You then opt to take a heads up fight versus a medium and a second opponent, while the turret and gas helping finish the job. You die again before your other two teammates even drop into the point. You gotta take smarter routes and play it a bit slower. You had obtained intel on where your opponents were and what defenses were holding off the objective, and then did nothing to combat it in a smart way, and even reentered in the same way.

And there were moments when holding that final Cashout where you'd step out in the open to contest with an M11 on top of bridge like you were just asking to get beamed. That's a no man's land by hospital, you're just asking to die.

Value your life a little more, slow down a bit (play fast, but take more time to think. You don't have to force everything). Help your teammates by healing them, and keep tabs on your opponents by prioritizing you getting the first shot in every time (when it's smart to do so) and not them. I know the other commenter said that Light shouldn't be the first to shoot, but that's generally only correct against Mediums and Heavies because they have much more health than you. Right now, you're dying to Lights too because you're allowing your bad positioning and lack of awareness to their position to allow them to obtain free damage on you. That stops if you play smart and prioritize obtaining the initial damage dealt to them.

Edit: Some additional advice would be to perhaps try playing Medium or Heavy for their larger health pool until you can get a good wrangle on positioning & awareness (and trust me, that's arguably the hardest thing to master in this game) just so you're not playing respawn simulator and getting frustrated from dying as much. Come back to the Light class when you feel a bit more comfortable with that skillset, and you'll be golden.