Ehm, once again no. Mayweather has far more screen time than Sulu. He has two character episodes while Sulu has none.
What is bland about having been born in space, grown up on a cargo ship and now serving on the first Starfleet vessel which explores deep space while you are the only one on it who has actually some (admittedly not so deep) space experience?
If you take the mere character setup and ignore the actual performances Mayweather is easily the most interesting human character on the show. But, alas, the guy couldn't act whereas e.g. Trinneer or Keating made far more out of characters which were at least conceptually (a relaxed Southern boy and a stiff Brit) less interesting.
We can also compare Uhura and Sato. Would you seriously claim that the latter character ho got more to say than "hailing frequencies open sir" is actually better? Do you seriously wanna go on claiming that ALL characters in VOY and ENT are flat while denying that TOS featured two undeveloped characters, Uhura and Sulu who got virtually no screen time or background? Hell, one of them didn't even get a first name in the show!
By the way, I don't wanna claim that all of this makes ENT kick ass and TOS suck. My point is rather that TOS worked despite of its abysmal non-troika major characters. Perhaps it actually worked because it only focused upon three instead of seven or more?