Well, you sound like a team player. You place the common good (fun together) higher than individual ambitions (or maybe place your own worth very low, I can't tell from one sentence, but the outcome is the same).
Saying deliberately sounds like it's not just a thing that you find yourself doing again and again, but a conscious choice. That suggests there was a choice to make; that the option of playing a self-centered character was something you were actively aware of, but were sufficiently repulsed by it to make a point of being better than those people.
I think you're a nice person, empathetic, while not so entirely innocent as to not even consider the possibility, still principled and caring enough to actively defy it.
To put forth a counterpoint, they could be afraid to express their individuality and use team synergy as a (albeit positive) mechanism of avoiding that.
Hell, that makes me think of myself. I hate playing tank in mmorpgs because they're always the leader in dungeons. They set the pace and have to keep aggro and proper boss facing and that's a lot of pressure I don't enjoy. I prefer healing because while still being a crucial and potentially stressful role, I'm not "in charge."
I appreciate that you took the time to supply the nuances I omitted. While there is value in a positive framing, it's important to acknowledge potential struggles as well. We can't effectively tackle issues if we're not aware of them.
In any case, while I'm not qualified to help you with your difficulties, I hope you find - or have found - a way to work on overcoming them. Dealing with insecurities, from my own experience, can be a tough process, further amplified by setbacks and a lack of perceived progress. But if you persevere, even if you might not feel that you have improved much, you may find yourself looking back at a time when it was worse and, by contrast, see the progress you've made. May that hope, that your future self will look back and be proud of your hard work, give you the strength to keep going.