1. Comics Namor did so because he was possessed by the Phoenix Force. Know the difference. This is the second time now you don't get his strategem. There would be no point in drowning Wakanda. It doesn't benefit him one bit.

2. And none of the demonic parties connected to the book were introduced in the MCU or are connected to their current plans. Not right now anyway. The effects of the Darkhold however are still being felt through Strange in his next movie connecting back to Clea and Dormammu, but we'll have to see there. That doesn't make it a weaker bit of material for having a different story. It just means you can't stand any form of unique storytelling.

1. I know he was possessed by the Phoenix Force but the reason why I brought it up is because even without it, it's something he would do. If he had that much power just in general, he would have done that. Heck he did more during the Incursions. Instead of talking it out, he destroyed inhabited planets. He called the Phoenix Force to earth know that it's an unpredictable force that mainly destroys so that he could tame it & he was ready to murder for it. Not ask for submission from others, he summoned it & as soon as someone got remotely in his was he was ready to beat them like a Cherokee drum.

2. Cthon is in the MCU, they said it.

1. The result of annhilating Wakanda is one less ally and a surface world more ready to see him exposed and killed. The way he does it brings in Wakanda as an ally forced to work with him out of sheer fear, and will keep his secrets to make sure of that. He secured the lives of his people with his only true major loss being some of his soldiers instead of everyone like you are suggesting.

2. So have many figures that have existed in the background of this universe and a part of the wider ancient history. It does not make Clthon a part of the immediate plot. As I already mentioned. The effect of the Darkhold is mainly going to be on Strange. For Wanda, she is switching back to heroics once again as an anti-hero upon her return.

MOM did not "Ruined the Darkhold". It's treated the Darkhold the same way it has always been treated in the MCU ever since it was introduce in Agents of S.H.I.E.L.D. It's possibly the best thing about that complicated Movie. Also, the Darkhold and Clthon can still come back later on just like the characters or the Stones can still come back. It's is a Comics series after all lol.

By the logic of MOM, it's not coming back & that's 1 of Cthon's most notable tie to the mortal realm. If I remember correctly he was only able to possess those who read the book so I need to read up on the ways he entered the mortal realm or how he was defeated permanently.

MOM stated that the Darkhold was a transcription of the writings on the wall of that mountain & with the original text gone the Darkhold was destroyed across the multiverse , as it stated in the movie.

Quantmania Kang or Loki's Kang could still have one in their Timelines. You really think Kang would let something that destructive be destroyed permanently?

It wouldn't make sense as to how they're able to keep it from being destroyed. They're not powerful enough to do something like that. With it being destroyed like that, it must be bounded by some kind of multiversal law. Kang & Loki in the comics don't possess power like that & MCU nerfs characters heavily so they dang sure can't do it.

The TVA Straight up nerf the Freaking Infinity Stones to make them nothing but paper-weights, I'm Sure A Kang can figure out a way to protect one Book lol.

Thanos

Every story downgrades their characters for the sake of what they are handling at the immediate moment of a different kind of structure in an adaptation. The Marvel Universe is no different.

In the case of the Infinity Stones, they are always nerfed outside of their home universe however.

As for the Darkhold, I mentioned Strange's corruption by it like three times lol