It’s an over simplification, but, I’d say that the following is essentially true regarding City and the jacks in the Premier League era - we were both as bad as each other from 1993 onwards, we were better than them in the noughties and they were better than us in the last decade, while in this decade, we finished above them once, they finished above us once and, although it’s early days yet, look like doing so again this season.
You said Swansea have been the dominant side in Wales for “the last decade at least”. I’d agree with you about the last decade, but it’s much more arguable when it comes to the “at least” part - certainly, any comparison which includes the pre Premier League period as well has to have us as the dominant side.