I think it depends on what you mean by equivalent. In terms of financial success, given the state of the DCEU's brand in comparison to Marvel's, yeah a John Stewart film probably wouldn't do as well as Black Panther. If we're talking about how it resonates, then I think it's more murky. Black Panther did as well as it did with black audiences (evidenced in the proportion of domestic ticket sales) because it featured commentary on the black diaspora and its relation to the African continent. It raised issues of heritage and belonging which definitely produced a paradigm shift in black pop culture and intellectual discourse. Funny thing is it didn't even have to do that because there are plenty of Black Panther stories that have next to nothing to do with race. But the character lends itself pretty naturally to those types of stories because his entire mythos is a subversion of white supremacy, colonialism, and other related topics.
The Green Lantern franchise would have a hard time telling a story similarly geared toward racial politics, but that's only a problem insofar as DC thinks that's necessary to make a great black superhero film. I'd have a problem if they were basing which black hero gets a movie on who can tell the "blackest" story rather than who can be used to tell the better story. Especially since casuals and fans (especially the "blerd" community) have been appreciating John even when he didn't have a narrative tied to his ethnicity. What worked for Black Panther doesn't necessarily need to be applied to DC's black heroes, especially when on a conceptual level a black-led space opera can make as many headlines as a black-led kingdom.
DC certainly could lean into different aspects of the GL mythos, using aliens as an allegory for race and things of that nature, but I don't think that's essential for making a John Stewart film that resonates with black fans or fans in general. In many ways his presence alone means something and what really matters is the quality of the story he's attached to.