Your timetable is far off.
there was over a year of releases between Necro 4 and the dark time. Highlighted by the Shroud. but Revers refuge was in there as well.
Titan was actually released in a worse state than Abbot. Abbot was beatable. and was beaten several times. just without doing the minigames.
Regardless... I've found U23 to be entertaining.
Content wise, I'd give it a "D". The 4 flagging quests are just rehashes with new mobs. no imagination went into the upgrades at all. The lack of LotD was a huge letdown as well as that was the highlight quest of od4 imo. the raid could of been a lot better as well.
that being said, Harper, PRR/MRR Changes and the loot overall make up for the bad content.