I wouldn't say it's weak to be somewhat traumatised after a sexual assault. I've heard a lot of people criticise the AR for various different reasons, but the one I agree with most is that on Buffy's show, Spike's attempted rape of Buffy is used mostly as a springboard for SPIKE'S redemption arc- rather than focus on how the victim has been affected (in this case, being the main character on the show), the show seems to focus on how bad the attacker feels about it. I don't think anyone wants that because they want to see Buffy brought low, and obviously people deal with trauma in a lot of different ways, but I can see why people were not happy with how the AR was dealt with, and how little of the emphasis in the aftermath seemed to be on Buffy.
Moving onto some more general points: On the matter of physical strength- obviously, it's not going to be a very interesting storyline if Buffy is stronger than literally everything that she comes up against. A big part of the story is how important her friends are to helping her survive as the Slayer- from helping her fight, to researching, to assisting her in areas that she is not necessarily skilled in herself. The whole of Sunnydale High assists in the battle with the Mayor. Willow, Xander and Giles combine their spirits with Buffy to defeat Adam. Anya comes up with a good deal of the ideas used to batter down Glory, Willow's magic helps to throw her off, too, and it is Giles who deals with Ben to prevent Glory from returning. Xander stops Willow from destroying the world, Anya stops her from killing Andrew and Jonathan, Giles delays her. Willow and Spike do most of the work in the S7 finale, and Angel provides the amulet for Spike. That's just looking at Season finales where Buffy has been assisted by others.
On the matter of emotional strength. Firstly, I think it's important to recognise that showing emotions does not necessarily equate to weakness. It's human, and it's relatable. As is having flaws- all of the characters on both BtVS and Angel are flawed, and I think it does make for more compelling viewing than a bunch of flawless heroes.
Taking the above into account, I don't think it's necessarily a bad thing for people to want a lead character with flaws, or who is sometimes physically outmatched, and is forced to look to other ways of defeating her opponents. I think it's people wanting realistic characters.
All that said, however, I do think some of the examples you give- wanting Buffy to be with Vampire X, because Vampire X deserves it, for example- are definitely dodgy. I have posted before in another thread about "Characters A and B should get together because A really wants to be with B!", without mentioning whether it is actually what A wants, but just to repeat, it really annoys me. And I'm not sure that Spike should be weaker than Buffy- yes, he has killed two Slayers, but both looked like fairly evenly matched fights to me, and doesn't Spike basically say in "Fool for Love" that he won because "all a vampire needs is one good day" (i.e. better training, luck, the element of surprise, whatever...) rather than "Because I am awesome and totally stronger than a Slayer"?
In summary, I can understand why people want Buffy - and any lead character - to have flaws, and show emotions. I don't think that this is a particularly sinister thing in general. Though there are certain complaints that seem to indicate that people want Buffy to come off weaker so that another character can look stronger, which irritate me.
