I think neither slayer respected Wesley, but for slightly different reasons.
These are all great points!
For Buffy it was mostly because he wasn't Giles and didn't share that already established Watcher/Slayer relationship that they had built between them during that first couple of years. Add to that her general disaffection with the Watcher's council after her surprise Birthday-fight-to-the-death-thing.
I think this is an important aspect of working with teenagers that the internal Watcher's Council has never quite figured out, and probably why their slayers tend to only live a couple years before ultimately being killed. Giles initially was like this too. In the first episode, it is clear he is doing his duty, as charged to him. He didn't really want to be in California, and he didn't understand Buffy as a teenage girl. But you can see a shift in him throughout the first season, where he begins to understand the important aspect of building a relationship with her, and allowing her to have relationships outside of the Slayer-Watcher dynamic. This is starkly contrasted by the Kendra/Zabuto relationship, in which she was sent to him at a very young age, and that was the extent of her social circle. Because of this, she died relatively quickly in her duty.
For Faith, she was just much further down the disaffected path; the council clearly didn't care for her or value her (that includes Giles) so why should she obey any of them them, or trust them even?
I think you raise a great point about Giles and his (lack of) relationship with Faith, though not entirely his fault alone. The council plays the largest role in Faith's downward spiral. They sent her a watcher to Boston, and that watcher died. Then, they never followed up. Giles, as the resident watcher in Sunnydale, did take her under his wing to train, BUT he stopped short at providing the relationship with her that he gave to Buffy, and even to the rest of the Scoobies. Giles and Willow had a solid relationship. Giles clearly never "liked" Xander in the high school years, but he still established a sort of relationship with him. And he even extended this to caring about Cordelia and Oz. But other than being a "tool," I don't see Giles really establishing any true type of relationship with her.
For all her snark Buffy still did what Wesley wanted in 'Bad Girls' (with the tacit approval of Giles of course) but Faith was just full-on 'screw you I'll do what I want' and only turned up for the assignment in the end because of Buffy.
Wesley reminds me of first year teachers. He thinks he has to come in hard and strict, and does not understand the relationship-building aspect of being a teacher. Especially with teenagers. I actually like the dynamic between Giles and Wesley, because it reminds me of a first year and veteran teacher relationship, where Wesley tries different strategies and goes to Giles for support. But, to Wesley's credit, he was not adequately prepared to handle a slayer like Faith. He was screwed, just as much as she was. The council was probably hoping that Faith would be killed quickly, and they could get a new slayer, similar to Kendra, on their side.
However when Wesley appears to Buffy in 'Graduation Day Pt. 2' as himself, not as a representative of the WC, she gives him a fair shot in helping them, which is telling.
I think being "fired" by Buffy really put into perspective his shortcomings as a watcher. And you can see this continue in his interactions with Faith in seasons 1 and 4 with Angel. I often think of Wesley as more of Faith's watcher than Buffy's for this reason. Buffy's true watcher, even at the end of season 3, was Giles. There was never a true replacement. But Wesley, even though he lost her in season 3, was always Faith's watcher, and Faith clearly sees this as fact, because of her hatred and target of him in season 1 of Angel and then their resolution in season 4 of Angel.