Think you guys are reading more into this than there actually is to it.
They need an audience-proxy character to basically be told what's going on and why. Said character obviously cannot be offed until they've finished being Basil Exposition, meaning that they are going to get a fair amount of screen time. Using Johnny in his typical goof mode kinda makes him Jack Burton (BTILC) and would have a major impact on the overall tone, making him the hero wouldn't be ideal either as it risks being very Chuck Norris.
Basically its a crutch for sloppy writing, where they are basically creating a character to fulfil a certain function.
Note the quote is "white actor be" not "white actor play" the hero of the story, very significant.