How have the fragile Naaru lasted this long?

[Kraddark]

I agree with you.

With Malfurion I think there's one thing holding him back. Well, he is the oldest emo mankind ever known but honestly, I think it's his fear of his own power. I'd believe he fears he may lose control like Illidan (we kinda know that Illidan didn't lose control of his power but from Malfurion's PoV it may seem so). And there are only few things that will drive him to using his actual power.. for example, if daddy Cenarius is in danger or, especially, if sweet Tyrande is.

I do think a major failing of Warcraft's writing is their constant introduction of powerful npcs. Players start to wonder: "Why doesn't Illidan come handle this?" It wouldn't be a problem if they accounted for every single godlike being and gave us a plausible explanation for why they're busy but with so many moving parts it becomes unmanageable.

It gets worse when NPCs come in and "save" the players (ex:Lich king and Tirion).

[Zulkhan]

Blizzard always finds ways and excuses to incapacitate Malfurion to not let him have any major role in game. For Legion, it's "His tie to nature and the dream is too strong, so he is extra vulnerable to the nightmare". I still don't understand why he doesn't help fight the legion. He gave the command of the dreamgrove to the player then just disappeared.

They find excuses because it's a less drastic route than outright retconning the character. It's a wild guess but I think Blizzard is regretting to have let Knaak to turn Malfurion into some stupidly overpowered character as these are the consequences: a character so stupidly powerful that you have no idea how to handle without him wrecking half of an expansion by his own, inevitably doing a strong disservice to the character as all that power ends up having no role in the story and so the character itself.