Yeah, I didn't do many changes except a bit in the descriptive texts mentioning the deep dragon and the dracohydra. I updated a few statblocks to make them a bit more aligned with the new changes in certain abilities (change shape, legendary actions, etc.).
Funny thing about the Aspect of Bahamut. It has a mythic ability called "Celestial Shield (Costs 2 Actions). The aspect manifests seven spectral ancient gold dragons around himself that protect him; he gains 77 temporary hit points until the start of his next turn." But no spectral dragons in Fizban's. Probably a typo they should have said ghost dragons? That or they missed referencing MME3.
And yes, it's possible the gem dragons (in MME age categories) will appear in MME4. We'll see.
I think the Spectral Gold Dragons are fluff that do nothing but give him 77 THP. They don't need stat-blocks.