I found that attitude a little bigoted and narrow-minded of her. Buffy seemed to think that Riley's success as a demon fighter had more to do with the experiments that Walsh had conducted on him than his ability to fight demons. I can only wonder if Whedon had allowed the audience to realize that Buffy's viewpoint was wrong by allowing Riley to successfully deal with the vampire that had wounded her in "Fool For Love" and the vamp nest without the Scoobies' help.
In fact, I have never understood the current thinking that Buffy always needed her friends by her side to deal with supernatural bad guys.
Characters like Spike and many of the series' fans claimed that Buffy was successful as a Slayer because she allowed the Scoobies to fight with her. Yet, the Scoobies were with Kendra when the latter was killed by Drusilla in "Becoming, Part 1". They were ineffective in that episode. Buffy had to do without the Scoobies' help on more than one occasion - especially in her fight against Angel in "Becoming, Part 2" and her successful snatch of the scythe in "Touched". And in "Fool For Love", Riley certainly proved that he didn't need the Scoobies.
I suspect that deep down, Buffy never really knew Riley or even bothered to get to know him. I believe that she had viewed him as some kind of object - her Joe Normal guy - so that she could pretend that there was something normal and safe for her to cling to. I think that by S5, Riley knew her better than she knew him. But . . . Riley had failed to communicate with her at a time when he needed to.
Why do people try to turn Riley into some kind of sexist? I never thought he was one. He seemed very comfortable in taking orders from Maggie Walsh. If anything, I think he was too inclined to put her on a pedestal. I think that Riley was a little disconcerted by Buffy being stronger than him . . . at first. But as I recall from S4, he seemed more shaken by Buffy's challenge to Dr. Walsh's authority and the authority of the U.S. Army, later in the season. As for S5, I believe he began to suspect that Buffy never really loved him and may have used him as rebound. This seemed to have become more apparent, when Buffy began treating him like a china doll following his operation in "Out of My Mind". He should have said something or protested against her treatment of him. Instead, Riley made one of his biggest mistakes and remained silent until it was too late.
And if there is one thing I have to admire about Riley, he has never tried to make choices for Buffy, using "the greater good" as an excuse. This is something that both Giles and Angel have been guilty of.