The sorcerers from Kamar Taj have never been on the level of the "Avengers" in the MCU. When Thanos was doing his thing during the finale of Endgame, while the crew showed up, it was in support. Wanda, Thor, Tony, Cap, and Carol are the only ones who were seen as capable of fighting Thanos and only Carol was really able to press him. When Strange, by far the most capable wizard of the group, fought him in Infinity War, he got stomped out by Thanos in less then a minute.
So in this flick, the crew they run into did what the 616 Avengers couldn't. Beat Thanos "properly". Thus setting them up as well above anything Wanda would have faced at the point. That she bodied them turned her into the unstoppable horror movie monster they were looking for.
You don't have to agree with anyone else on this subject nor like it. But I think there was a clear narrative reason, and that doesn't mean I slept through the movie or don't understand how to watch them.
Well, none of those comments about being asleep were aimed at you, and actually weren't about being asleep while watching Dr Strange &TMOM. I was taking that other guy to task for ignoring some stuff in Infinity War and Endgame.
Anyway since you're here, I invite you to consider the following and how it answers your " clear narrative reason" for the Illuminati's appearance. Ready ?
Okay, here goes. This movie is about Dr Strange and how he deals with the threat posed by Wanda.
We see Wanda wipe out Kamar Taj, and beat Strange and Wong pretty easily - she's proved her point, he knows that he absolutely cannot defeat her. Even the mirror dimension won't stop her.
Now if Strange actively went looking for help from the Illuminati or other powerful heroes to help him, and Wanda wiped them out, that would serve some small story purpose.
But no, the writers aren't that clever. He essentially meets the Illuminati by happenstance, and then they die. The Thanos in this universe must have been a total mug to get beaten by such a bunch of arrogant idiots.
This is just Marvel showing us some shiny objects, member berries if you will. They add nothing to the story by being there and Wanda killing them adds nothing to the story, because we already know that she can beat Strange and Co, which is what the story is really about.
She doesn't need to show us how much more powerful she is by killing a bunch of other superheroes...because all she has to show us is that she can destroy Strange, America and Wong( which she's already done).
So, what does it accomplish ? Nothing
She's already proved that she's unbeatable for the purposes of the characters and the story.
We don't need to know that Wanda is so powerful that she can beat the Illuminati, because in the overall arc of the story that doesn't matter at all. Apologies, I'm repeating myself here.
Contrast the Illuminati's appearance with the appearance of Garfield and Maguire in No Way Home . They have character arcs, and make a real contribution to the story, and it's outcome. That's an example of a real narrative reason for them being there.
The Hulk's appearance in Thor Ragnarok is a similar proposition.
Want a test, to see if what I'm saying holds up?
I know what a huge fan of logical reasoning you are. So, apply this question:
"If the Illuminati had not appeared in the film, would it have made any significant difference to the outcome ?"
The answer is clearly "No". You could delete the sequence in which they appear, and the Book of Vishanti as well, (because it has zero impact on the outcome) and you could still easily get to the same ending.
That cannot be said for Maguire and Garfield, again, because they serve a real narrative purpose.
It doesn't bother me one iota that the Illuminati are in this film, or that people enjoyed it - if that's what people like, fair play to them.
What I take issue with is the pretence that the Illuminati's appearance was anything more than contrived fan service. Just own it, it's there to suck in fans and for the moment seems to have worked.
You might also ask yourself about the logic of being told a character is the world's smartest man, and then seeing him tell a dangerous enemy almost precisely how to destroy a teammate ( or why Black bolt's sonic blast didn't simply burst through the soft tissue of his face rather than bounce back and explode the back of his head, or erupt out his nose ?) Or maybe why Reed, again world's smartest man, then decides the best thing to do is try to grab Wanda Or why his teammates stood and watched him being turned into spaghetti....or how the invulnerable Captain Marvel is incapacitated by a falling statue. Just a few things to think about.
If you think, even a little, or apply a little logic that whole sequence falls apart really quickly.
Again, that shouldn't diminish your enjoyment of that sequence - if you liked it, fair play to you. You got your money's worth and enjoyed the film.
Why not just admit " Hey, it was fan service, and I don't care, it was awesome." ?
To be honest as much as I felt it was contrived, I really enjoyed seeing Wanda wipe out those arrogant jerks. I wish she'd made Captain Marvel's head explode after that " We can take care of your little witch." comment.