Agree, I can't speak to Morrowind, I've never played it, but Skyrim's dungeons are certainly quite a few steps above Oblivion's. Were some parts of SK's dungeons repetetive? Maybe a little, but certaianly nowhere near as cookie-cutter as Oblivion's. Overall ,Skyrim's dungeons are a huge improvement.
Oblivion did the Ayelid ruins right- applying the word "cookie cutter" to them is not the best way to put it. Unless you think they are all the same because the walls are all the same color, that was pretty boring, They had great geography/construction on the map, and were certainly certainly NOT cookie cutter. I believe the first one you do when you get out of prison had 4-5 levels down into it? Not identical to any others of course.
Oblivion had the problem with forts/caves being extra lackluster, and instead of Draugr boring us to death it was probably goblins.