Despite changes over recent years to "welshify" Cardiff... to me, it essentially feels like an English city. Barely any different to Bristol over the channel.
If you look at surnames of people living there, and exclude those who have moved more recently from other parts of Wales... the vast majority of families have roots in England.
Culturally Cardiff feels very different to other bits of Wales, even those 5 miles into the valleys feel so much more Welsh.
The Cardiff accent is mainly an english accent, especially in the nicer areas and the older generation sound almost RP.