My problem Cray wasn't so much that no one "helped" but rather no one seemed to try to help. Almost everyone seemed content with letting Graham do all the work. There was little feedback of the co-ordinated effort and other then the freekishly helpful genie most characters you see were either "Thinking" or trying to keep everything together (Heck I highly suspected Edgar was secretly doing something and still do)
I distinctly remember Graham turning down offers to help from certain people who offered. "No, you have to take care of blah blah blah."
Also I assume Oberon, Titania, and Edgar both have their full compliment of magical power. (Heck Edgar was almost on par with Malicia)
Yes, Edgar was almost on par with Malicia.
In Etheria. Etheria is an entirely different realm of existence. It operates on a totally different set of rules. The entirety of KQ7 only takes place in about ten minutes in our time, for instance. You can't assume that because something is one way in Etheria that it will be that way in Daventry. On Earth (well, Daventry) he has displayed exactly zero magical power. Even helping Rosella escape from Lolotte -- nadah. You're making an assumption based literally on nothing and then holding it against the game.

You know what they say happens when you assume!
You are forgetting that this is Kings Quest and magic isn't the solution to everything even magic. There is no doubt in my mind that were everyone together their full compliment of magic wouldn't undo the curse.
I'm not forgetting that, but what we know about Oberon and Titania is that they're not very effective at much other than powerful magic. They're not effective leaders (they allowed their whole realm to turn to pot without ever noticing while they searched for their son), they're not effective adventurers (they had no idea what happened to their son, even though investigating why their kingdom was turning to pot probably could have clued them in). In TSL we learn that they're seriously co-dependent on each other and not exactly emotionally stable (really, you enchant your entire realm to forget about your child when he disappears? Graham and Valanice had the same thing happen
and their kingdom got invaded by a dragon and lost their other child and handled it better than that.)
So, what I'm saying really is.... without their magic, how can they help? None of their subjects are here, like not even in the same world as this is going on. I think you're just saying all these people could be helpful without actually examining what we know about them and what we've seen them do (and
where!)
"Who's kind of busy with her coma to get in touch"
Honestly I just assumed many people were just too busy. I also highly suspect this wedding was rather sudden.
You would think Genesta would have been invited anyways. I imagine she can teleport herself places, not just Rosella. Maybe they had a falling out. Maybe Genesta hates weddings. I don't know. Point is, she's probably the most likely to be able to help.
If you are comming up with lists of people who could have possibly helped who weren't at the wedding. Celes the goddess of nature would have been a rather big one, The Standing stones who are as old as the earth itself, The Good fairy who can give one protection from evil, Queen Mab (sorta, we already got a spoiler of why she couldn't have helped), Curtis, really just about anyone from KQ7.
I accept your challenge!!

-Graham's Fairy Godmother (KQ1): mysteriously absent since Graham took the crown. But she probably could have helped, yes. Even though I think if she showed up now Graham might have some words for her.... about, y'know, "WHY DIDN'T YOU STOP ANYTHING ELSE? EVER?!" Worst fairy godmother in the universe.
-The Good Fairy (KQ2): nobody knows even who she is -- she appeared, cast her protection spell, and vanished. She could probably help, yes.... if anyone knew how to find her.
-Brother Fragola (KQ2): according to KQC he even moved to Daventry after KQ2, and I bet he knows a thing or two about curses. Given his lack of presence at the wedding though, he either died of old age (or something) sometime during the course of the series or he's in Daventry.
-Genesta (KQ4): this one I will agree, almost definitely could help somehow and I'm wondering where she is.
-Crispin & Cedric (KQ5): Also rather glaringly absent, but not as likely to be able to help as Genesta in my opinion (though it seems like Crispin is a Silver Cloak given his relationship to Mordack).
-Cassima (KQ5/KQ6): she's holding the kingdom together in time of crisis, that seems helpful.
-Ancient Mariner (KQ5): I bet his medical knowledge would be able to make Rosella and Alexander's comas much more comfortable at least.
-Hasan the Ferryman (KQ6): he's helping by ferrying you around everywhere.
-Harun alRaschid (KQ6): "poofed himself into an aardvark in the end" (I just put him on the list because I love that line

)
-Shamir Shamazle (KQ6): he is doing his research -- which is proving to be extremely helpful -- but he's also capable of teleporting people places at least around
this world (as seen in the good ending of KQ6), so it makes Hasan seem less important and it makes Genesta and Crispin's absences even more peculiar.
-Archdruid (KQ6): he did his thing, I don't think he could be more helpful than just providing lore for us.
-Lord of the Dead (KQ6): he probably could help if we mess up further down the road but not yet!

-Lord Azure (KQ6): far too snotty to help.
-Oracle of the Winged Ones (KQ6): I think she did what she could to help.
-Rosella (KQ3-7): in a coma.
-Alexaner (KQ3-6): in a coma.
-Valanice (KQ2-7): cursed.
-Lord Attis (KQ7): in Etheria -- we don't know where the portal currently is or where it comes out or if Etherians have any power in our world, so this is incredibly iffy.
-Lady Ceres (KQ7): in Etheria -- again, we don't know if she could help at all in any way.
-Lady Mab (KQ7): spoiler aside, she's got her own realm of existence even further removed from us than Etheria, and I don't think she can leave it. Furthermore, the dreams the twins and Valanice are having are caused by the curse, so I'm not sure she has any power there.
-Weaver of Dreams (KQ7): even if he weren't in Etheria, I seriously doubt he would help. It took an awful lot of convincing to get him to help Valanice.
-The Four Winds (KQ7): I'm like 99% sure they can't leave Etheria what with being the wind there. Could be wrong. Not sure that they could help anyways, they mostly just move fast.

-Wizard of Daventry (MoE): I think we all want to ignore that he exists. Like, really, you only managed to half shield yourself from an impending doom you knew about? What a putz. Anyways... he probably
could help though, even though he's in Daventry.
-Connor (MoE): he's sworn to guard the Realm of the Sun, I expect he might be hard to reach even for Shamir Shamazle. Plus, he's mostly good at kicking butt and taking names. And not being able to reach things. None of that sounds helpful.

I don't know what Standing Stones you're talking about (they sound awfully stationary though) and I don't know who Curtis is either. :\
Anyways, there's a few people who I'm positive
could help and aren't.... but they're not even in the game. I think your basic premise that the people we meet in the game could be doing more to help is flawed though.