Warning! Spoilers for Dragon Ball Super chapter 75 ahead!
Vegeta may have just created and achieved the Ultra Ego transformation on his own, but recent extenuating circumstances prove it couldn't have happened at a more tragic time in the Dragon Ball Super manga.
Vegeta currently finds himself in the midst of a fierce battle against Granolah, the sole survivor of the Cerealian race who were all victims of a mass genocide perpetrated by the Saiyans as they endeavored to expand Frieza's empire long ago. Granolah proves himself to be quite a handful for Vegeta and Goku early on, after using his planet's Dragon Balls to become the strongest warrior in existence. The rampaging Cerealian easily bests Goku and then quickly turns his attention to the Saiyan Prince who has no choice but to unlock Ultra Ego, a form that combines his most terrifying qualities with the boundless power that Ultra Instinct provides without relinquishing all control over his body.
By chapter 75, Vegeta is ostensibly on the path to defeating Granolah until the Saiyan Prince realizes that he has sustained too much damage and resorts to a villainous last ditch effort by employing one of Frieza's most dastardly strategies to finish the Cerealian off. Granolah not only deflects Vegeta's attack, but reveals that their fight has just awoken his true power, leaving a stunned Vegeta to watch helplessly as his enemy dramatically approaches him in a menacing manner. Even though the Ultra Ego transformation initially seems to have finally established Vegeta as the hero for the first time instead of Goku, it's obvious that it comes much too early in the fight for this to happen.
Dragon Ball Super's formula for final battles usually involves Vegeta fighting an enemy first. Then, once he has been bested, Goku steps in and saves the day. It was therefore exciting when Vegeta encouraged Goku to face Granolah first (to which the latter quickly obliged) because it was assumed that he would lose and then Vegeta would have to take over. However, there was a major caveat, which chapter 75 has now justified. The current arc literally just started and couldn't end so quickly. Both Goku and Vegeta were destined to lose during this first confrontation so the saga could continue.
For Ultra Ego to have truly made a massive impact, the Saiyan Prince should have unlocked Ultra Ego during the last round of the final battle. But because Vegeta had transformed, fans felt that this moment had the potential of being Vegeta's big moment. But by transpiring now, it only serves to further fulfill his ongoing role as a tragic hero. Vegeta is a Saiyan Prince who was born destined to be the strongest of his kind and possibly the first to achieve the highly coveted Super Saiyan transformation. And yet, Goku has bested him at every turn, even becoming Super Saiyan first. Because of what is required to achieve Ultra Ego, it's unlikely that Vegeta will undergo another awakening like this any time soon.
Dragon Ball Super's Galactic Patrol Prisoner Saga is the most recent example that best mirrors Vegeta's current predicament. Near the end, Vegeta bests Goku in a stunning way by mastering a technique known as Forced Spirit Fission that Goku was unable to learn even though he had more time to train. And yet, Vegeta is still cast aside during the final battle against Moro, whereby he uses a reversed form of Forced Spirit Fission to help Goku beat Moro. The fact that Granolah looks to have defeated Vegeta now, despite the Saiyan Prince having created own transformation while Goku has relied on a preexisting technique, negates the impact that Ultra Ego could have made into nothing more than a failed attempt. Time will tell if Vegeta gets another shot in future chapters of Dragon Ball Super