After all the snickering about Welsh Govt’s intention for “world class” South Wales metro services, you suggest in your posts that Cardiff’s heavy rail cross-city network not merely world class but in fact the “perfection” which Paris RER and Crossrail can only aspire towards.
The location of Cardiff's HR stations long pre-date the formation of the Welsh Government and the Labour party itself. As was explained extensively in the Metro thread, Cardiff is a compact city with crowded streets.
Cathays services the University, Welsh Govt civil service and the civic centre.
Queen St serves retail and offices.
Central serves the Stadium and the numerous office developments going up in the vicinity, as well as a new college.
Ninian Park serves Cardiff City stadium.
All are 5 - 10 minutes walking distance maximum.
Put trams on Cardiff's narrow, crowded streets and there's no way you'd get from Cathays to Central and out the other side on your way to Barry/Penarth in under 10 minutes.
Cardiff is in no way comparable to London or Paris in size. Be sensible.