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I think you aren't necessarily the best person to evaluate yourself. Unless you are some kind of superior human being.

Is 6 years enough to think they won't improve?

What's your point? That it's not a skill? Having a system behave acceptably as it grows does not count? Getting paid for it does not count?

Fine. Don't do it. Wait till you get a certification. No one's forcing you to think about these things.