100% of people can reach max gear, but people create their own limits holding them back. If you only choose to pug, not forming relations with other players, those you can rely on to run with together regularly, learn each other’s play style, help others gear up not just focus on your own. Yeah that means giving up items you got to give another player to help them to help you.
Player attitudes to another person is also crucial, the best groups when they do something wrong, make a mistake, or wipe they don’t start talking each other down or throw insults at each other. They get up, rebuff, and go again. They talk it out about what they can do next time, try different strategies. What we failed today is a learning experience for the next time not rage-quit after 3-4 wipes, you keep going until you learn how the other in your group play, help them out, and make it repetitive clockwork.