1. "Images flashed through his befuddled mind again. Landscaps, creatures, artifacts. Krasus had witnessed time in its ultimate aspect, all at once.
Aspect? That word summoned another read vision, one he had thankfully forgotten until now. In the midst of the swirling chaos of time, Krasus had glimpsed a sight that left his heart and hope shattered.
There, in the center of the fury, he had seen Nozdormu, the great Aspect of Time . . . trapped like a fly in a web.
Nozdormu had been there in all his terrible glory, a vast dragon not of flesh but of the golden sands of eternity. His glittering, gemlike eyes, eyes the color of the sun, had been open wide, but had not in turn seen the insignifficant figure of Krasus. The great dragon had been in the throes of both battle and agony, ensared yet also fighting to hold everything together--absolutely everything.
Nozdormu was both victim and savior. Trapped in all time, he also held it from falling apart. If not for the Aspect, the fabric of reality would have collapsed there and then. The world Krasus knew would have disappeared forever. It would never have even existed"
2. I have never objected to Nozdormu being one of the high tier entities of Warcraft. He can create pocket dimensions, can kill a person thousand times over with a single thought and do so in different ways, he has the ability to see ALL things that has and will come simultaneously, enter the mind of others, create time and space vortex, uses fatal magic across dimensions and his gigantic size alone could easily par him with Archimonde as he climed the World Tree. Not to mention that he has every single power any bronze dragon has ever shown.
3. The Titans does not travel planets to destroy corruption. You have gotten that wrong. They travel cosmos to spread life. That is the reason why they left guardians on Azeroth (The Aspects). Highfather Aman'Thul granted Nozdormu the powers he did, and Nozdormu became the most powerful entity on Azeroth, and easily among the top 5 in existance. I would even be so bold as to say that he is the second most powerful there is, only surpassed by Highfather.
(This is of course relative. He is as powerful as he is because he is a master of time and space. An advantage in combat impossible to fight)
4. There is one point of high importance that you need to consider: Highfather is no destroyer. He is a creator. Nozdormu is no warrior. He is a guardian. Sure, Highfather could probably dominate the universe if he ever wanted, but he only wants to create. The Pantheon are no warriors.
5. Nozdormu's feat of holding everything together is, indeed, the greatest accomplishment in all of Warcraft after Highfather, who created time.
6. The universe itself is the reason. As one Bronze Dragon said, if certain things in the past are altered to a drastical extent, it would not alter the future. It would create no future, or any past. All that is would cease to exist. The Old Gods were trying to escape their banish with the usage of time disruption and altering of the ancient war. What no one knew but Nozdormu (Who was trapped by the Old Gods), was that the fabrics of reality (Again I want to refer everyone to professor David Deutsch's book named "Fabric of Reality"😉 was being torn asunder, that existance would cease and that time was crumbling.
The Bronze Dragonflight was given a HUGE responsebility.
7. I imagine that Nozdormu has a lot of options: He could create extreme mental pain that has her lose focus, he could compress Ultimecia to the point of no existance, he could turn her into dust by making her body beyond ancient, he could transform her into a baby, he could ensnare her with telekinesis and let lose the wrath of time on her, or he could appear before her and with a grip crush her (For as far as I recall, she is not that big and has not shown much physical durability). I even think that Ultimecia might lose against Nozdorm in an actual time battle. Other than her compression ability, has she shown anything to be on par with Nozdormu?