He created 4 alternate realities and merged them in one panel. Kismet also mentioned that he warped all reality to draw her out. He also made Superman feel multiversal madness and dispatched infinite versions of linear men with a gesture. Not to mention, he merged himself with the universe becoming the illuminator of all realities iirc.
Uh, what? So you're saying that Jamie should go to sleep to win this battle? So that leaves Dominus (an active player) vs a sleeping Jamie. Guess who will be considered the winner in a forum fight? Also no, it can't be resisted through sleeping, it merely hinders his most go-to tactic, he can still warp reality around a given person. Not to mention that he was weakened when Superman defeated him.
You realize this has nothing to do with the four realities he created, right? This was the multiverse madness showing. Yes, in that instance, he merely let Superman experience a multiverse of madness.
The four realities which he created previously, were real though. It was outright stated that they were not hallucinations:
"A being who can, at a whim, pull the reality carpet out from under us." According to Superman.
Dominus could also merge with the universe. Actually he could have done that whenever he liked but he wanted to kill Kismet first, and when that was no longer an option for him, he casually merged with the whole universe.
The "multiverse madness" as you call it that Superman is experiencing is the moment of the "four realities". Those around Superman are not experiencing it, only Superman and him experiencing it is what we see in that scene.
Dominus's bios repeatedly declare that he uses his continuum control to warp reality. This is something the Infinity Men themselves do below:
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Even when he himself increases their numbers and then reduces them, he is doing so by picking them from various times:
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His reality warping is linked to time manipulation and access to the mind and memories of his target.
I'm not sure how such an exploitable weakness is irrelevant. While unable to access Superman's mind, he is able to warp the immediate area solely for the sake of trying to distract Superman, but can not affect Superman.
Lot's of characters are major reality warpers. That doesn't make them multiversal.
Where does it state that he merges with the whole universe?
The four realities are merged by dominus in superman #138 (in previous superman-related issues, he was experiencing those realities). Then Dominus confronts kismet who flees from him in that same issue. The comes Adventures of superman #561 where Dominus disguises himself as waverider to learn where Kismet fled, and only after that comes action comics #748 where the multiverse madness showing happens. So yes, it is most definitely a separate instance.
And is there a reason why you simply ignored Kismet's comments? She outright said that they were real and that Dominus actually warped reality.
Nobody denied that he was using temporal manipulation in that specific showing. However he has warped reality several times throughout the arc.
So Jamie goes to sleep, which leaves Dominus as the only active player between the two. Leaving Dominus as the winner. Is that more to your liking?
It was shown on panel for one. And secondly, he states that he has taken Kismet's mantle as a cosmic force (universal embodiment) in the universe when we see him merge with it. It's quite obvious what was going in those pages, actually.
Those three issues seem to cover different aspects of one long warp until the real Waverider appears at the end of issue #748 to see Superman caught up in it, as shown.
I'm sure I stated earlier that no one is saying that he doesn't warp reality.
Right. Mostly using temporal manipulation (which is how he warps reality).
Does Superman go to sleep?
That's a pretty liberal extrapolation from art. Kismet was not a universal embodiment during that time. Busiek sort of shoehorned her in to that role years later. Before then, she illuminates paths.
Dominus is one of the most exaggerated characters in comics and due mostly to Superman fans because of the need for him to have beaten a multiversal power. Problem is that I have yet to be given a demonstration of such multiversal power. Manipulated timelines and a pocket dimension the he resides in doesn't cut it.