Season 5 was filler once the first episode was over with. What they should have done was this:
Go right into the Brother Sam (Mos Def) storyline from season 6. You know, the one that showed character growth and gave Dexter a dilemma. They abandoned that halfway through season 6 and i say it should have been spread throughout season 5 until the last couple of episodes. They had Dexter's brother become Dexter's dark passenger but after that amazing reveal at the end of the episode where Brother Sam was killed, they only used him for one episode and played it for laughs. It should have lasted at least a few episodes, taking the fathers place in that role. It should have led to Dexter going evil, killing LaGuerta in the season 5 (not 6) finale. And THAT is when Debra finds out who Dexter really is. Not with that predictable, cliche, see it from a mile away twist that involved Tom Hanks' son. The villains in seasons 5, 6 and 7 were so random. They needed to make Dexter the villain with his dead brother in his ear. There's no way to top Trinity, so don't try. Get away from the formula.
I would have sprinkled this season with Hannah in a similar way to season 7 but the idea would be to have Dexter torn between the dark side (Hannah who understands that side of him) and Brother Sam (who is trying to save Dexter's soul). Sam is murdered by somebody connected to Hannah. Dex learns that Hannah's not actually behind it but proceeds to go on a rampage with the Ice Truck Killer constantly telling him what he wants to hear. Quinn and LaGuerta would be suspicious of Dexter. It leads to them investigating the death of Brother Sam and the dude Dex drowned that night. Quinn backs out last second because of Deb but loses her anyway. This leads to LaGuerta's death like i said, when she doesn't back down from trying to arrest him. Deb walks in on the scene of the crime. Cliffhanger (pretty close to what actually happened. Maybe it still takes place in a church).
This would have set up the final season. This is so simple and logical. How do you screw this up!? The final season (season 6) should have been the hunt for Dexter with Debra torn between helping Dexter get away and turning him in/executing her brother. Batista, Masuka, everyone should have found out and picked sides. Every character is put in a bad position. Dexter begins to fall in love with Hannah, and sees who she truly is, which is one of the only things they were doing right in the final two seasons. She helps him get rid of his dark passenger completely.
The finale would be what the original showrunner intended. Dexter on a table this time. Lethal injection. Cameos with all of his past victims (Doaks, Lila, Miguel, Trinity and more such as Rita/Brother Sam) all returning. Hannah leaves with Harrison beforehand to live a happier life.