Indeed, there are many people who do not want to carry the heaviest load. But I don’t think that makes a difference here.
The ‘thou shalt’ of the camel is not necessarily coming from ‘the moral God’, as you’ve been using the phrase, as a slave morality. A slave morality can after all not transform into a master morality, since it is is ones nature. Rather, the camel holds the spirit of reverence. This can be reverence of anything great, of the world, in general. The camel still sees the value of the world as outside of himself, the metamorphoses are steps into internalizing the value. The phase of the lion is where the notion of value has been internalized, but the actual substance of the world has been rejected in order to make this step. The Child merges with the world as himself. He is reconciled with the fact that what he is isn’t the whole world, but that his greatest knowledge and highest value is in his total participation. This is against the pride of the lion, who rather holds back, who holds on to the pathos of distance to secure his pride.
the Child sees not difference between him and the world - his pride is not in his superiority over the world, his pride is like a sun, his pride is not in his roar, but shows only in the clarity and strength of his deeds.
Firstly, what makes you extend the notion of the dragon to a kind of internal demon of the lion? I can not find reason for this in what you quoted or highlighted. But, assuming that there is reason for this, to answer the question: because the spirit is overtaken by the spirit of lightness. The dragon just vanishes, if the spirit is fortunate (well-constituted) as its work is done. It is only a relatively ill-constituted spirit, which may account for the majority at the stage of the Lion, that holds on to the dragon, because the inner dragon, or inner demon, or forceful virtue, seems to the spirit to be the power of the spirit itself.
I don’t see that Nietzsche has replaced it - to me they are different passages, with different meanings.
The meaning may correlate in part, sure, and it is possible that what you quote here has sprung from the thought in the note. But the note is the topic, and I think it describes himself. Perhaps he ‘replaced’ (falsified) it later because he was fearful of what he saw.