You do if you are sitting at the same table with Captain Marvel every week.
Or lets take it a step further, Superman.
Now a character can always have their side plots and personal goals, there is always a way to make things interesting. But if we are talking about the main plot....power imbalance can absolutely skew the spotlight towards a single character if unchecked. I used to love the Justice League cartoons, and there are lot of fun fights where the whole league is beating up the bad guys. But....realistically if only superman was present....the result would be exactly the same. It would take maybe a few more seconds to finish the job. The rest of the league could literally just grab a chair and hang out, and the result would be 100% the exact same.
Only in those rare cases where someone throws out the red sun or kryptonite is another leaguer really necessary, or if the plot is such that multiple leaguers are needed at the same time (and normally this requires you to nerf super speed to make it plausible).
This actually happened in a 3.5 game I played it. My friend played a dread necromancer, and "won the game". His army of undead was superior to everything the rest of us had, and he could heal them at-will. Every enemy we killed just added to his collection, the strongest the monster we faced, the better the undead he got. Eventually one player just flat out said in game "I think my character would just quit at this moment, I honestly don't think I matter to the campaign". And in that game....he was right.
Now I don't think most games get to the level, and I think 5e's balance is such that's its very difficult to get to that level of imbalance, but yeah if that imbalance occurs....it does suck to be the guy next to superman narratively speaking.