Timm pitched an episode where Terry kept letting Dana down, but in the end he did something big for her. He wasn't sure what it was or why it was so important, just that Terry finally came through for Dana when it mattered. Burnett took that and had it so Terry didn't come through and (presumably out of the blue) Terry and Max start making out at the end.
And you're misunderstanding my scenario. She's not getting her own show, she's being built up as being part of the Bat-family for an episode, then at the end decides it isn't working out, strikes out on her own, and she's never seen or heard of again. You'd consider that disrespectful and a betrayal, right? You thought she was finally getting the appreciation you've wanted her to have, then at the last minute it's yanked out from under you, the show tells you it wasn't meant to be, and it's as if she never mattered. That's what the rewritten pitch probably felt like to Timm.