Would it be fair to say this origin of Namor is unique for the Marvel film universe? My comic knowledge of him is rather limited, and I agree that for movie purposes it was very well done.
My only nitpick in terms of his writing is I felt the movie did a great bit of worldbuilding in having Namor show Shuri his undersea empire and try to genuinely persuade her why an alliance would benefit both realms, because they share many qualities that isolate them from the surface world. Wakanda had a similar crisis in the earlier movies, when T'Challa had to balance the knowledge of how Wakandan resources could benefit the larger world (while also potentially making it easier for that world to see Wakanda as an ally) with the risks of those advantages also being abused, if only out of fear or good intentions that misfired. And it's a nice parallel to Shuri having to struggle with her own rage against the human world, the part of her that wants revenge even if it's the wrong path.
But when Namor later meets with Ramonda, he doesn't share any of that expanded context or try to persuade her the same way. He just blatantly threatens Wakanda and even the possibility of harming Shuri, who is potential leverage as well as perhaps a future ally. He's clearly smart enough to understand that Wakanda could be a more serious threat as an enemy than other nations, as well as a powerful ally, but this just seems a bit odd.
Also, was it ever explained how Namor and his people were able to avoid detection during their incursions into Wakanda? I do recall during his initial appearance, he somehow evaded
all forms of detection rather conveniently.
Overall, I enjoyed the film. I'd definitely say it's one of the darker, more mature chapters in the Marvel film universe but not in a bad way.