I didn't dislike the first ending. It made sense to me. This whole season, especially his son coming back defeats the whole purpose of the last 3 seasons of the original series.
The ending is just bonkers and I wont even bother putting it into words because there's just too much wrong with it
You can also interpret the ending as Harrison being a really deranged individual which was messing with Dexter from the start and could have easily planted the screws from Matt and instigated the whole investigation of Dexter Morgan by Angela when he accidentally implied to Audrey that Jim wasn't his real father's. I didn't like the fact that Angela suddenly turned into Sherlock Holmes.. Which could be explained by Harrison subtly hinting at something weird and pulling the strings from behind Dexter's back.
This could explain all the inconsistencies of the writing of Harrison to a degree. It's also implied at the very end that he had the letter that Dexter wrote to Anna explaining why he left in the first place. So Harrison knew from the start the reason his father left. It's also implied Harrison was in town earlier than initially thought when they show that person in the bushes when Dexter was near the white deer. Harrison might have also seen Dexter kill Matt. Maybe Harrison even killed Anna to begin with.
Besides if the whole purpose of the ending was that by killing Dexter, Harrison would become "free", then I have to say that makes no sense whatsoever. If Harrison was a normal person, I can't imagine killing your father in cold blood would ever make anyone healthier.
This is all speculation because the writing is all over the place and not very conclusive.