I haven't played WW HD but based on the gamecube version I would have to agree. The ability to parry made it unlikely for an enemy to hit you in a one-on-one fight, and then you throw in all the items that somehow make the combat even easier. IIRC the boomerang will stun anything other than a covered darknut, and the grappling hook often gives you hearts from enemies. I think it's fair to say that this is the only Zelda game in which I felt completely safe from death the entire time.
In terms of puzzles this also has to be one of the easiest games as well. For instance I feel like the big mirror room near the end of the Earth Temple was designed to be one of the hardest mental challenges in the game, and I don't know if it's fair to even call it a puzzle since all you have to do is push things along preset paths and shine light on things. I do recall getting stuck in places though, but not more than in other Zelda games. The thing that often gets me is whenever you need to use the Deku Leaf to glide later in the game. I always forget that the item even exists since it's unique to the game.
In terms of achieving 100% I would have to give this game some props for all the collectibles and especially the figurine collection. This is a really time-consuming game to 100%, and I would think it would be extremely difficult to achieve without some sort of list of all the things that need to be done. This is probably the hardest Zelda from the 100% perspective.
In terms of minimalist or three heart challenges this would have to be one of the easiest if not the easiest game. In terms of a minimalist challenge this game is easy because there is so little that you can skip. I think the helpful things that are skippable include most of the bottles, the magic armor, and the hero's charm. For three hearts this game would naturally be one of the easiest because of the combat being easy. I would actually consider OoT to be easier for me at least, but this is probably due to me having more experience with that game.
