I agree with all of your points (although I will admit that I'm HYPED for this movie), and dunno why you got some harsh criticism for an opinion, but this one right here (in bold) is the kicker. Unfortunately, Disney/Marvel put WAYYY too much faith in Jonathan Majors as Kang, and the whole incident with his gf tanked a lot of stuff. However, they should've just stuck with a recast... I don't know why they're so afraid to do that, especially when Don Cheadle cooks better as Rhody than Terrance Howard. So much potential...
As a result they decided to add in Doom. I seriously doubt Feige when he said they "always" planned for Kang Dynasty to transition into Doomsday. It's clear they knew how much they messed up.
My main gripes with how this movie handles Doom comes in three fashions. Will his backstory and motivations actually align with how the MCU is currently articulating the route of the story, and does the mask stay on for 99% of the time? Yeah, Doom has his mask get taken off in both runs of Secret Wars in marvel comics, but it being RDJ kind of showers doubt in there. Lastly, I do know that the team announcement a week ago showed Doctor Doom's name as "Victor Von Doom", but there's still a connection between Stark and Doom according to the Russos. I just hope it's not something like "Oh! MCU's 616 Iron Man was actually a variant of Doctor Doom" or something crazy.