This may be the single worst casting decision I have ever seen.
I have seen casting bad actors for great roles, I have seen great actors cast for the wrong roles, I have seen controversial actors cast in roles endangering the film, I have seen actors cast in movies where they actively hate the project and it shows.
I have never, never seen a casting choice that simultaneously ruins a character fans have been waiting for decades for, AND diminishes the legacy of one of the all-time great fictional characters/movies and endings AND conveys an utter tone deafness about what the audience is looking for AND conveys a humiliating level of desperation.
It doesnt matter if he is good in the role or not, he will be seen as an Iron Man variant, or be compared to Iron Man, or it will be weird when the characters DONT compare him to Iron Man - meaning Doom and his impact and legacy are already in the shadow of Tony Stark - diminishing YET AGAIN one of the all time great comic book villains - and worst of all diminishing the one villain fans have been crying out for a decent portrayal of for decades.
THEN there is the fact this completely undermines the ending of Endgame and the awesome culmination of the only 10+ year dozen film multi-billion dollar saga in cinematic history.
THEN there is the fact that this just SCREAMS - we are going full tilt into the multiverse stuff despite EVERYONE being over it by now.
THEN there is just the reality that this move signals loud and clear Marvel's panic and desire to replicate its own past successes in the most pathetic way possible.