I liked the stuff with Wes (and you could still do that no matter the character's role), but I agree with the other points. Yeah I don't see why she couldn't have been CEO from the start. You could still have had the rivary with Lindsay too.
My GUESS is that they knew they wanted someone close to betray them for Lindsey, and it would be too WTF for Lilah to do that (because of Lindsey), and also not anything of a twist (it would actually be a twist if Lilah was loyal to Angel and company, and in that case would make it harder for characters to "stumble" along into the messes they did).In fact I don’t even know if there is a reason about why in season 5 we have Eve instead of Lilah. I completely don’t understand the writers ! What did they think ? I mean from a scenario point of view, Lilah as a ghost could be the relation between Angel and the senior partner. It’s really stupid to not have taken the opportunity. Did the actress want to continue in the series ? I try to find a reasonable reason which would explain why they didn’t keep Lilah.