Hakka is definitely one of the 7 major Han dialects of China.
so called hakka chinese is a linguistic window to "middle chinese" which was the official archaic chinese language spoken in sui, tang, and song dynasties. when mongols conquered china, old mandarin was forced upon many parts of china, but southern enclaves of refugees and survivors from older chinese dynasties retained much of the original xi-an and lo-yang tongues (mostly shaanxi and henan) and southern dialects. over the centuries, middle chinese disappeared and/or it merged with southern dialects and blended into obscurity. today, there are various offshoots of hakka: for example taiwanese, fujian, guangdong, guangxi, guizhou, sichuan, and hunan. this proves that hakka was a widespread language spoken in a huge geographical part of china, mainly in the south because the north and northeast were overrun by mongols and manchus respectively separated by five hundred years of devastation. the manchus, in the qing dynasty, was responsible for the propagation of mandarin, which was the main beijing dialect, to the rest of remote china including the south. beijing was the capital of the mongols under the yuan dynasty.
if you're good with linguistics in the study of consonants and vowels and tones, you'll notice that hakka is mutually unintelligible from mandarin but is closer in many pronunciations to middle chinese. also check up the rhyme books of tang. rhymes are secret codes to breaking the language mystery.
hakka is a real survivor and descendant of the true ancient chinese language and should be taught and preserved, although the hakka of today is a far cry from the language spoken by the first survivors of sui, tang and song. mandarin is a bastardized language of invaders, traitors, arse lickers, lackeys and cowards under the mongol and manchu yoke. and hakka shouldn't be called hakka or kejia. it's a fucking shame that the original people of china are called "guests". it should be called fak-yu.