In defense of Season 7 Buffy, I feel it important to point out that she never wanted or volunteered to be the leader of the group. Nobody else was there to do it, it had to be done, and she was the only one who even made an attempt to bring some degree of order into the mess that Giles dumped in her lap, then went running off to collect more Potentials. Buffy did the best that she could with her limited resources and considering the fact that she was one girl, no matter how powerful, standing against an army of Bringers, another army of Ubervamps, a psychotic, super powerful serial killer, and a being who personified the very essence of evil, I, for one, think that she did one hell of a job. As allies, she had a construction foreman, a brat kid sister, a "wicca who won't-a," an ex vengeance demon, a former criminal mastermind, and an ensouled, half delusional vampire who was at times under the control of her greatest enemy. Add to that, she had to hold down a job as school counselor and support a house full of strange teenaged girls. A load like that would break the strongest back.
Buffy did the best that she could with the resources at her disposal. If she had no experience as a general, neither did anyone else, including Giles, in the brief periods when he was around. Add to that, she got little to no support from the people who were supposed to be her friends, her mentor joined forces with a vengeance seeking phony high school principal to murder her strongest single ally.
Certainly, Buffy made mistakes. Her first, and biggest, was to establish from the very first that, if she was going to be the one giving the orders, then the orders that she gave weren't subject to popular vote. Get to it, or get out. That simple.
The particulars of her final plan about returning to the vineyard was never actually revealed, so we really don't know whether or not any of the Potentials would have been at risk, or not. I personally believe that Buffy would have tried to keep their risk at a minimum, but we will never know, since no one even gave her the courtesy of hearing them. We do know that she eventually did return to the vineyard and was successful in retrieving what Caleb was hiding there. For all that we know, that could have been her plan from the beginning, with everyone else creating a diversion nearby. But that's just speculation on my part.
The single biggest mistake that Buffy made in the whole campaign was in not having a private conference with Willow, Giles, Faith, and Spike, (Xander was in the hospital at the time) to explain her plans, work out the details, and be assured of her team's support. THEN, she, with them backing her up, could have explained to everyone else exactly what was going to happen, why, and how.
Yes, Buffy made mistakes in Season 7. Yes, quite a bit of her success was due to dumb luck and sheer audacity. But who among that little group, given the resources at hand, could have done even a little bit better?