A system that's balanced so that players can make any choices they want and not worry about overshadowing others is a worthwhile goal, IMO. If a system does allow character builds that overshadow most others, it's true that you can remedy that by having every player voluntarily avoid those choices. But I see that as the players working together to fix a flaw in the system, and it's better if the system doesn't have that flaw to start with.Are players who are taking these feats aware that they are taking spotlight away from other players? If so, why do they continue to choose these feats, or having taken them, choose not to use them to act in service of making other characters shine from time to time?
Is this a case where we must change the rules to save players from themselves? Or might we expect they'll voluntarily make choices that don't overshadow others to the detriment of the game experience?
Requiring players to not only understand the choices relevant to their character but to also understand the entire system well enough to avoid overshadowing other types of characters is essentially requiring that players have a large amount of system mastery in order to make choices that will be fun for the group. Isn't it much better if players can choose anything they want without worrying that they'll break the game for others?
My personal experience is that GWM and SS do generate that feeling of overshadowing other characters when used effectively, and the game would be better if they were rewritten.