What is up with the uneven progression of difficulty?

I don't feel like the temples are ranged in order of difficulty at all. The Spirit Temple is the last temple, and it's the easiest one of them all, or at least for me it was. The Water Temple is the most challenging, and it's right in the middle. The Forest Temple comes first, before the Fire Temple, but I think the Forest Temple is more difficult than the Fire Temple. Obviously the order of temples is based on the events of the story, but one has to wonder why the creators made later temples easier than earlier ones, particularly the Spirit Temple. In most of the Mario games, the progression in difficulty is very gradual and effective. I think the difficulty progressed well in the very first Zelda, and in Majora's Mask. In Link to the Past it was also kind of scrambled. Do you guys feel the same way I do about Ocarina of Time, or do you think there was a gradual progression of difficulty?