So let me get this straight, the new T1C is basically gonna be rerouted to provide a faster connection between Aberyswyth, Carmarthen & Cardiff as NAT take over and provide a proper coach service rather than a service bus that, as good as Wright Eclipses are, is a joke for a 4h35m express journey; and another possible reason for avoiding Swansea is that now it will be a different company to the X10 service, it probably needs to steer clear of potential revenue abstraction for Swansea to Cardiff passengers.
And First Cymru's new T1 extension (T1S) seems to have new timings that would actually allow connection with the T2, improving North-South travel considerably, since that would mean people throughout Gwynedd all the way up to Bangor would be able to travel to Swansea much more easily! Also, Aberystwyth & Lampeter will continue to be connected to Swansea when the T1C bypasses the city! As for Lampeter to Cardiff, it would still be possible by using the T1 then changing at Carmarthen for the T1C!
Overall, this does seem to be a great improvement
and I see why they're numbered as they are now:
T1
C =
Cardiff
T1
S =
Swansea