In retrospective I think the main misconception is to think of Finn as a black character or a representation of black people as a whole. Yes he is played by a black actor but there's nothing inherently black about him. He is a fictional character who happens to be played by a black actor.
Han comes off as an alpha because even in the original trilogy he was way older than Finn. He was almost 30 at the time while Finn is 19. Change Han's skin color and age and we'll have almost the same character and almost the same complaints from the-never-satisfied-the-world-is-out-to-get-us-crowd. Why did Han had to be a smuggler? Why he shoot Greedo first, why did he got frozen in carbonite? Why didn't he escape on his own? I can see the whining no matter what character they had made black. There's not a single character in Star Wars that is perfect and that wouldn't fit in the-because-racism-narrative.
The way I see it there's enough space in fiction for rookies like Finn and badasses silent type warriors like Mace Windu.
I think its an issue of perspective. When you have so few characters black or non-white in these kind of films, or as prominent, then yes I think the one-or main-non-white character does take on outsize importance. With The Force Awakens Finn was the most prominent black character and there was one black female who has a backstory but I don't think she any lines and got an extended cameo during the destruction of Hosnian Prime.
I do think there was a lot 'black' about Finn, a distorted view of what black people are. His mugging, his bumbling, his incompetence, his deceit, and his love of white women (Rey), his being the comic relief, his willingness to forgo his own goals and sacrifice himself for white people. His being a janitor, a domestic, all of those are roles or ideas that have been ascribed to blacks in Hollywood. So to me whenever the decision to have Boyega play Finn I wonder if that led to other changes, or did how they eventually conceived of the character make Finn more amenable for a black actor? Even Lando with the pimp cape and the player persona, someone not particularly trustworthy, a shady-and unworthy-competitor for Leia's affections. And Samuel L. Jackson told Lucas he wanted to be in a Star Wars film so bad that he didn't care what role he played, even a slave. And Lucas thought he was hiding some old dubious stereotypes behind CGI and makeup with Jar Jar, Nemoidians, Watto, but he got called out for it.
Racism is baked into the cake of Star Wars. I'm not saying that its virulent or even always intentional, but Lucas drew on old Hollywood serials and stories, among others, and you're telling me that some of that source material was not racist? Heck, I think he even took the last big awards ceremony in the Rebel base in A New Hope from a pro-Nazi film or filmmaker. And JJ Abrams, while being a good director, doesn't seem to be that much of an originator. He's good at putting a film together but not so much with the vision or making a unique vision. He just combines old things in interesting ways at times. And TFA was just a regurgitation of A New Hope in particular.
I agree with you that there is enough room for Finn and Mace Windu, but the Finn pill would easier to swallow if you didn't have one main black character per each section of the saga thus far. If you have more than one, you can see other sides and other perspectives. Though I was better with both Mace and Lando than I was with Finn. Neither character was perfect, both had shades of gray, but so far they were more competent than Finn. I don't want a sweaty, stumbling, and bumbling black guy beside a kickass totally awesome white girl, a dashing super great Latino pilot, and a conflict, whiny, though he killed Han, white guy.
Your Han example to me illustrates that you got different varieties of white characters in the original series and throughout Star Wars, and movies/books in general. You got good, bad, in between, and you get tons of white characters.
Also, Han's age has nothing to do with his alpha male status. I'm sure you knew plenty of guys in high school or college, heck, probably earlier than that, that were alpha males. I do think Han's swagger does come from Harrison Ford, his matinee looks as well. Boyega is a good actor, but he's not a matinee looking dude. I mean they could've cast Michael B. Jordan for example and gotten perhaps a Ford or Billy Dee Williams kind of vibe, but they wanted Boyega because he was less of a sexual "threat". And some of us fanboys are eating it up, thinking they we are finally being 'represented', well I don't see it that way. It's the
kind of representation that I am more concerned about.
And your hypothetical scenarios we'll never know because Han wasn't played by a black actor. The closest we got to that was Lando and he was definitely a supporting player, and they couldn't even find a role for him to play in TFA.
Han did not shoot Greedo first, Lucas said it.