You don't have to act dumb (and you shouldn't). You just have to not act like a "rock star". The most brilliant devs I've ever met were people nobody would call "rock stars". They were collaborative team players.
This, exactly this. I know so many people who are "above average" developers that I would love to work with because they are nice, collaborative people that are a joy to work with. The biggest problems we've faced are with these so called "10x developers", who do get stuff done, but are a total pain in the a* to deal with!
A developer that knows how to treat other people in the team, knows how to be professional, works on what they agreed to during sprint planning, doesn't want to rewrite the project to a new technology and doesn't want to create their own cool project because they know the ultimate goal is to ship to users, doesn't react badly to criticism, is not unreasonably stubborn, has good hygiene, doesn't take code reviews personally and agrees that management has a necessarily different point of view from pure developers.
A brilliant dev is one who consistently produces solid and feasible solutions to difficult problems, in a timely way.
A more enlightening question is "what is a rock star" in my mind. A rock star is a dev who truly believes that they are the smartest person in the room, who looks down their nose at any work they didn't produce, who is only really interested in things that they think make themselves look better rather than things that will actually help produce the best end product possible, who insists on using the whatever latest shiny thing is in fashion over less shiny but more appropriate approaches, and so forth.
The Rock Star will say, “I will do these 10 things by next Friday.” And then next Friday rolls around and 8 of them are done. This repeats week after week, but I can never tell which 8 will get done. They’re boastful and proud that they got a lot done but the rest of the team can never count on them to get any specific thing done.
The other person will say “I will do these 5 things by next Friday.” And then next Friday all 5 are done. And they repeat this week after week after week.
I agree with your scenario, but I wouldn't consider someone who consistently under-delivers a "rock star."
This is why defining terms is important. For me, a rockstar is a developer who is just further along, who likes to program in their own time, who reads Hacker News, and builds projects on the weekends.
Within 5 years, that person will be much further ahead than the rest and will spot pitfalls, security, and performance issues simply because they have encountered them before. However, sharing that information could lead to that person being called a "rockstar" and problematic, hampering "progress".