Neither ScotRail nor NI Railways run cross-border services apart from to the first station across the border (Glasgow–Dumfries–Carlisle) and in cooperation with IÉ, although that's mostly a consequence of where the railways and borders are. Things might be different if lines such as the one from Melrose to Hexham had survived.
If anything, the odd one out for Wales-England services is currently Bristol as the only one without TfW.
If anything, the odd one out for Wales-England services is currently Bristol as the only one without TfW.