First post - I've been a reader for awhile, and I'm excited to join!
The focus of SS was sword/shield technique. Usually Zelda boss battles require the player to use the dungeon-item to attack the boss's weak spot; while this was occasionally true (Scaldera, Koloktos, Tentalus), fights with some mini-bosses, Molderach, Ghirahim, and Demise himself require NO items. Items were integral to progress through the puzzles and environments, but most battles, even with basic enemies, required skill with the sword/shield mechanic.
Demise is easy/hard based on a player's style with the fighting technology. If the player can shield bash, he can get in close and personal. If he can't so much, he stands back and dodges, using the Skyward Strike (which is what I ended up doing after bashing got me killed). Nintendo put its "final boss" chips all-in with its sword/shield mechanic, and it has produced the kind of fights that REAL sword/shield conflicts are. TP had to nerf Ganondorf's sword in order to make the battle longer - think Obi-Wan and Anakin (which was ridiculous and milked beyond belief). But a more realistic sword fight would be fast, messy, and possibly brutal. The first time I met Demise, I got my behind handed to me -- FAST. Then, I re-equipped and came up with a new strategy, and handed it back to Demise, just as quickly.
While I wanted more from the Demise battle, I appreciate its raw violence -- in a Zelda game that featured harder fights, it was appropriate. Not every game can end like a Final Fantasy epic, nor can every game end as perfectly as OoT.