IV: You are sooooo right about that! Nevermind that their accent & expressions were diluted by a major Italian immigration back at the turn of the 20th century. What's even more puzzling are some I've met that bristle at being referred to as "Latin Americans", claiming to be "Europeans" instead! Don't get me started on how they corrupted & incorrectly incorporated the vosotros form of the language...!
So many interesting points on this. Yes, you're all right on the heavy Italian sound of Argentine Spanish .... BUT, I've found that in Spanish, there is a wider gap between spoken and written Spanish, including in newspapers, than in English, especially American English.
I've found La Jornada has the most colloquial Spanish among Mexican newspapers (not talking about its politics) while the broadsheets adhere to more formal Spanish, though I'd like to hear what the native Spanish speakers say.
If you go back and read American papers of the late 19th and early 20th century, they're written in the formal or what I'd call stilted style, at times almost incomprehensible (to me). Not me, but American literary "experts," (not folks I'd like to share a life boat with) give Twain and mostly Hemingway the credit for revolutionizing written English to adhere more to the spoken language.
Will I get into trouble for saying that many folks describe many great modern Spanish writers as "flowery" in their style, anathema in English? Hit me, Spanish speakers. Anyway, that's why, perhaps, Argentines and their Southern Core cohorts can attack Mexican Spanish, thinking they'll find allies in Spain, because they think their written language follows more to traditional Castilian? Again, Mexico is confirmed as the largest Spanish speaking country in the world, and isn't it the strongest and largest economy in the Spanish speaking world (?). The majority always wins in language wars.
(I also read three Brit dailies daily, and while they're trying to get as breezy as American newspapers, their prose often follows Dickens a bit too much, I find. Canadians more conversational, Aussies almost as well. Can't help it. I'm a news junkie. I should dedicate myself to more uplifting activities.)