I get from your points that you believe that MCU Thanos is going to be identical to the comics character in every way, but I just realistically don't see that happening. There isn't a single character in the MCU to date that is completely identical to their comics counterpart, especially the villains. Loki, Hela, Killmonger, Zemo, e.t.c are all villains that diverge quite significantly from their comics counterparts in backstory and motivations to various extents, because the MCU have to adapt them in a way that fits in with
this universe and everything that has come before it. Key word here is 'similar'. Look at the dictionary definition of the word similar - '
having a resemblance in appearance, character, or quantity, without being identical.' Jim Starlin can still feel that the writers have done Thanos justice by capturing the general spirit and essence of the character rather than doing a literal page to screen adaptation of him, I think even he would likely realise that it's just not feasible or practical to adapt Thanos completely accurately from comic book to movie, which are two very different mediums. Thanos waxing lyrical to a mute female in a hooded robe who is literally Death itself in disguise works perfectly within the greater context of a comic book, but will it necessarily work or translate well to live action? Especially in a movie that is going to have precious little time to develop the multitudes of characters it has to juggle. Or would it perhaps be better to put Thanos with a character that actually has a personality and responds back, and is more of a foil for him in that regard? I don't get the whole, 'Thanos and Hela never could have met' thing either. Comics Thanos is immortal and thousands of years old so MCU Thanos feasibly can be too. Hela travelled across the Nine Realms and quite possibly the rest of the cosmos with her father during their conquests, so they easily could have met or come into contact with each other prior to her imprisonment.
For all we know, we could be coming at this from completely the wrong angle. What if we're both right in some way? What if Hela did really die at the end of Ragnarok and underwent some form of transformation? What if Death itself then decides to use Hela's physical form as an avatar? That way it kinda explains all of the above, including the no casting news and why there are so many subtle little clues to be found about Blanchett being in IW? Who the hell knows? I can't wait to find out though.

t: