What makes Great Weapon Master and Sharpshooter so good?
The answer is the way bonus damage is multiplied through multiple attacks.
I think opportunity cost and overkill make an impact on the value of the feats but the fact is that a fighter who takes two weapon fighting style and the dual wielder feat is far behind in average damage compared to a fighter who takes great weapon fighting and great weapon master with the advantage being a point of AC for the dual wielder.
It's counter-intuitive to look at a twf build (which is fine on some classes) and expect a bit of a defensive build instead a damage build. S&B expect lower damage for higher defense.
I find internet complaints can get over-stated and I find 5e generally good to the point I can play any class and I know I will enjoy it but no game is perfect. TWF is the poster child for fighter discrepancy in that regard.
I let champions who take twf as the first style take improved twf (house rule) for their second style for two off hand attacks on one bonus action because I think that gives the twf fighter a more viable option for the style.