My bad; I should stop overestimating people, but it will not happen again: Promise.

You also said "the" Southern dialect is the "largest" English one, which is dubious at best. When that doubt was noted, you doubled down by switching the topic from dialect to ACCENT (which is a different thing) and saying the Southern accent (which ONE?!) is most like Victorian English and thus probably most like British English (good luck convincing anyone outside or even most WITHIN the US that the British speak "accented US English.)and modern Englishare : ONE Southern dialect.

When discussing "ya'll" v. "you guys" etc. it comes down to dialect; accent is a(n irrelevant) question of how to pronounce words like "tomato" that are spelled and used the same in all English dialects. It might be wise to consult Wikipedias authoritarian lingual scholars further before proceeding further here. Either way, while majorities on half of all continents use English as a native language (and the majority of at least one more speaks it,) "ya'll" is rarely found outside the Southern US (ironically, the biggest exception is in urban US areas, largely due to the Great Migration from the South.) In terms of accents (once again) only ONE of many Southern accents is even remotely like Victorian OR modern British English, and that particular "Southern" accent is closer to New Englands, Britains and South Africas than to ANY other Southern one.

Just treat "dialect" and "accent" like "patriotism" and "proof," declaring them redefined however serves your preferred worldview.

Edit, because I forgot to mention: Those OTHER three continents where majorities speak English, even if not as natives? Guess which dialect AND accent most of the instructors demand all students use. Hint: NO American one. Also, another example of the difference between dialect and accent it that, while the word has existed for centuries in dialects throughout the UK, Queen Victorias famous apocryphal line is not "We ain't amused," because that word was beneath the lips of even most of her SERVANTS. This is probably a good place to stop digging.