A few Reasons why (well it is just excuses though hehehehehe)

No gorgon sisters because I couldn't really get the timeline of one piece in its real direction but since he is in a multiverse or so please just think that this one piece arc is in a one piece parallel world without them as I didn't really like them much or just that they are side characters and part of the mob that was outside the bedroom in the 18 plus chapters for one piece arc (muahhaahahhahaah anyway I am The author I am GOD yo what I say is what it is, so fear me mortals!!!!)

He is better than kaido when in xiantian because he already passed humanity by that time Houtian is the peak that humanity can reach and by reaching the peak of the peak of humanity he was already equal to Kaido in his human form and in xiantian his body strength isn't really needed much anymore but rather how he uses changes like changing into something harder than Kaido like the 4 pieces of red indestructible stone that gives the map of the final Island in one piece which even Kaido couldn't break.

Passing of core formation

Void core starts first because that is when he can make a core with his own space creation inside before that he is just manipulating space elements of the worlds his in and with increase in realm the space becomes more stabler and harder inside while demi god realm is when he can make a planet or a small world inside the void cores he makes.

God realm Before Undying is because in god realm he can start making cosmos and universes instead of just planets but can still die when his soul is attacked while undying is when he becomes the lord of the multiverse and technically one with the multiverse as long as the multiverse exist he will live even if his soul is extinguished and when the multiverse is gone he will naturally disappear along with it of course with all the gods and below those realms inside the multiverse. Which gives the detached or eternal a reason to be detached from the entire multiverse so that when it resets or disappears they will still be safe and can make their own multiverse again and again.