I'd chalk that up to self-interest rather than how most people actually view it, even if he believes it.
I'll reiterate that I'm not interested in an imitation like that either, especially since J'onn can pass as whatever is en vogue at the time-- Not a choice real people have.
John Stewart getting powers again makes me happy. Especially New God-esque powers, wow, it's like Kyle Rayner's Ion thing.
Metaphors for minorities in fiction (even if they don't always hold up as well) are pretty common, so I think it's the intention and execution that's important at the end of the day. Even if J'onn can shapeshift he can relate to feeling like the "other" and dealing with various concepts of identity and how that contrasts/conflicts with others and human society.
Of course I think it also all comes back to how definitive Carl Lumbly's portrayal of J'onn was in JL.
And funnily enough both Phil LaMarr and Carl have played family or fellow martians to J'onn in different adaptions.
Actually DC Comics actively and intentionally resisted the inclusion of black characters in specific and non-stereotypical POC in general throughout the silver age and well into the bronze because they thought racist southerners wouldn't buy comics featuring those ethnic groups. At the same time MARVEL was embracing the social zeitgeist in the USA, DC was digging in its heals to resist that progress.
using weird-colored aliens to fill the minority gap wasn't a creative decision. MULTIPLE creators tried to make the necessary inclusive changes, only to have them slapped down, erased or modified by editorial.
this was likely due to the changes made to the JUSTICE LEAGUE animated series to be more inclusive than originally designed both on screen in interns of hiring voice talent. By the time the live-action version was being reintroduced (also on a show that had lost its sole black character) the concerns of TV production had pushed the need to add some color.
At the end of the day, being Black is a mask J'onn can take off whenever he wants--and he does so when ever he's in battle anyway. Like Cyborg, I don't think DC's premier Black hero should look monstrous, while the White characters look like Greek gods.