^messed up priorities.
Finally saw the finale, which means I can actually read this thread now.
Deb finding out is long overdo. She's written in the show as a pretty decent cop, so to have her not know all this time strains credulity. But remember that in the last season she catches Dexter and Lumen (Julia Stiles) killing the kidnapper/rapist (behind a curtain) and lets them go. So, there's already a precedent of Deb letting a vigilante go. Of course, she may come to find out that it was actually Dexter behind that curtain. We'll have to wait and see if the writers sweep this revelation under the rug with some lame excuse or fully address it.
As for Laguerta, she's clearly written as someone who "plays the game" because she has to. I think it was established pretty early that she was the first Cuban/female lieutenant? I'm not exactly sure on that, but she's had to fight an uphill battle to get recognized, which explains her actions throughout the seasons. But really, she's just part of the supporting cast, so you can't expect her character to be fully fleshed out. The show revolves around Dexter, and to a lesser extent Deb, the rest of the characters are mostly fluff.
I have noticed the writing dip over the last few seasons. Seasons 1-2 and season 4 simply can't be topped by any other TV show, period. Season 3 simply had a weak story arch, but the character development was fine. Season 5 was meh and this season was painful in a lot of places. The last minute of the finale made up for it, though.