Please don't get me wrong. I know which bosses are optional. My little endboss rant and the comment about the save points near the jelly king are two completely separate issues.
I mentioned the giant enemy crab to contrast with the jelly king. (I have a habit of moderating my own arguments with contrasting examples) Of the two, I only found the King Jelly save a bit annoying, even though both didn't have saves down the corridor. But even then it is only a minor issue. One could argue that it is a part of the difficulty you need to deal with if you opt to fight King Jelly.
The lack of a save before Creator form 5 is my biggest real peeve. I actually liked form 3 and 4 in combination with form 1 and 2, it provided a nice break where you could fight the end boss, without actually "fighting" in the classical sense of fighting end bosses. But form 5 is very difficult, in the sense that it requires a lot of the traditional "gaming reflexes" to deal with him. I wanted to see the ending, but I failed at defeating form 5 several times in a row, and then having to redo form 1, 2, 3, 4, became a bit like grinding your CRPG character.
Continuing the game boss discussion: (I hope it is not to off topic for this forum, but since I started it anyway...)
I don't think bosses need to be replaced if removed, one could easily opt to end a story without one at all. If you reached the end of the game, then you have beaten the game, why is there a need for a big fight? The whole journey to the end of the game was one big undertaking in and off itself.
Imagine a story of a dictator who needs to be defeated, what will happen is that the biggest fight take place at the start of the active war, at some point, one of the sides has managed to gain control of a couple of key locations and defeated some key enemy units, or a certain amount of them. That is when the enemy has lost. Then comes the mopping up part, or maybe the peace negotiations. This could still hold an interesting plot, there might be some personal scores still left to settle, there might be a couple of guerilla groups left to take down. Game wise, some of the most difficult fights (for the main character) might still take place here. (they just don't need to be bosses, they could be hostile terrain with a couple of very nasty mooks)
The plot could still hide some darkness, one could still uncover some horrible crimes that have been taking place, during the dictators reign.
And to top it off, you could could still end it with a confrontation with the dictator himself. Just that, he is a politician, not a fighter. He used to have others fight for him. So instead of an end boss fight, the story ends with a short emotional dialog. If the writer is good and particularly nasty, he may even construct it so that due to the dictator his last stance (he would be a manipulator, not a warrior) the player is left wondering if defeating the dictator was actually a good idea. If he shouldn't maybe joined his cause instead!
Then you could still have the player kill the dictator with an attack, but as stated, he isn't a fighter, so he should go down with one strike.
Also, I do not think that everyone will skip boss fights, even if there is no in-game reward at all, some people will think it is fun seeing if they can defeat something challenging . And even if most people end up skipping the difficult fight, so what? It is only a very small part of the game.
EDIT: And sorry for the long posts. I didn't mean to create a wall of text, but sometimes I get a bit carried away with something. If anyone thinks I should have this discussion elsewhere, please say so.