Personally, I can't see a reason to keep a fiah in a tank it will be uncomfortable in, especially when there are alternatives that would be much more comfortable yet create the same effect. Also, tanks that small with fish that big tend to not only have water chemistry and gas exchange problems, but they also don't have a very good aesthetic. I had several large sunfish in a 125 gallon and it still looked crowded, especially when you factor in the cover you have to provide for a fish in that situation.
Very good point about creating habitat... most of us are actually not trying to keep a pet in a cage (a glass with water in it cage)... what we are all really trying to do is to create a little piece of the wild in our otherwise controlled world (heck, some of us are maybe even trying to control the wild a bit by bringing it inside, but that is too psychological for a fish forum).
But if creating a little bit of the stream/pond is your goal, then you need to add all the other elements, habitat, etc... and you need to recreate the scale and relationship between the habitat and the inhabitants.
Great thought there Yeahson