While I am not personally struggling or butt hurt with the casting of AE, I would be willing to bet that if there were another actor out there who looked, acted, and sounded exactly like a young Billy Dee Williams (as much as AI resembles Ford) and that actor actually played a "younger" Billy Dee Williams character in a previous movie, it would be a topic of much discussion. It's just not the case with Glover and the Lando role and the discussion is not even worth comparison.
This is a unique and rare situation in my opinion. I don't think most people who feel this way about AI are expecting Hollywood to always cast an actor, who's portraying a younger version of an established character, with such an uncanny resemblance.
I recognize that physical and verbal similarities are not always necessary. Ewan McGregor sold me as a young Obi-Wan Kenobi despite not really looking like Alec Guinness and having only a generically similar speech pattern / accent. I only look at the AE / AI discussion from a personal fanboy point of view. For me, seeing AI in those Age of Adeline clips made me believe I was watching a young Harrison Ford. And quite honestly as a huge Star Wars and Han Solo fan, the idea of him as Solo seemed just a little more magical.
But........it doesn't prevent me from seeing AE's performance objectively and it certainly doesn't automatically preclude me from believing he is that character.