What are your favorite movies, songs and books. If I said they sucked because that movie is only 1:30, the song sucks because it's only 3 minutes long, or your favorite book sucks because it's only 295 pages, would that make sense to you? How do you rationalize that length is relative to quality?
Ninja Theory has said they expect it to be 7-9 hours. That's fine. I expect upon replay, it will be even shorter. But what does that matter if the game delivered is focused and enjoyable? Would adding fetch quests and checklists increase the quality of the game, in your opinion? I'm fine with filler being cut out for the sake of delivering a more focused experience. I have little patience for filler any more. The repetition of the same "sidequests" or grinding for hours to increase skills doesn't do much for me these days. If you like that stuff, that's fine, but not every single game needs filler to extend length to justify a purchase.
A lot of people have complained about the expected length and really, what does it matter how long a game is? It's a baffling subject among gamers. You take this mindset to the discussion of any other medium and I don't think you'd get anywhere with it.