Look. I don't particularly like S5-6 Dawn. In fact, I hated S5-6 Dawn.
Yep, she was particularly terrible. Talk about
les enfant terribles.
She was EVERYTHING Buffy wasn't, and then some.
She was basically "useless" and the epitome of "that brat of a younger sister".
But. One needs to keep in mind 3 things.
1. She's the
only other person, apart from Xander, who isn't "empowered" at all. This in itself is a source of great frustration to Dawn, and causes her to be the "great unseen". No-one sees things from her point of view, it's always about Buffy, forever about Buffy. (Yes, I know, the title of the series is... BUFFY the Vampire Slayer, so it's supposed to be that way.)
2. She's also particularly unhappy with the fact that she's absolutely USELESS. It's not her fault, she can't do ANYTHING at all. It's an inferiority complex, and it's hardwired into her by S6, and lays dormant in S7 and S8. In fact, compared to all the characters, only Xander's lost more than her, all aspects covered.
3. She can't rely on anyone, long-term.
Tara died.
Willow estranges from the rest in S8.
Buffy's (almost) never there. Though Buffy's absence is understandable, it doesn't make for a good relationship.
The rest don't care about her, or treat her with kid gloves.
To quote:
Excuse me, she's been abandoned by about six parental figures. The girl has huge issues.'"
(Joss Whedon, responding to "Dawn is whiny" comments)
Or maybe this quote would make more sense:
DAWN: (voiceover) He [Xander] says I'm like a kid sister...
XANDER: (looking at the game board) Here comes the judge!
DAWN: (voiceover) ...but sometimes when he looks at me, I feel like he sees me as I am... as a woman.
And of course:
XANDER: Yeah. They're special, no doubt. The amazing thing is, not one of them will ever know, not even Buffy.
...
XANDER: They'll never know how tough it is, Dawnie, to be the one who isn't chosen. To live so near to the spotlight and never step in it. But I know. I see more than anybody realizes because nobody's watching me. I saw you last night. I see you working here today. You're not special. You're extraordinary. (stands, kisses her forehead, starts to walk out of the room)
DAWN: (tears welling in her eyes, calls after him) Maybe that's your power.
XANDER: What?
DAWN: Seeing. Knowing.
XANDER: Maybe it is.
Look, we've been seeing everything from Buffy's view.
It takes a non-empowered person to see another, to understand another.
(And besides, MY younger sister is WAY WORSE.)
😉
So, I'll say that, yes Dawn's really terrible at first, but does get better, way better than Buffy or Willow or anyone else, if only they didn't have powers.