What’s that got to do with it?
When you bought your Two Together Railcard, presumably the 09:27 hadn't been added to the timetable yet, and you were prepared to pay the £30 price for a Railcard that wasn't valid before 09:30. In other words, you were prepared to wait until (around) 10:00 to take a train from Carmarthen towards Swansea.
The introduction of the 09:27 doesn't change anything in that respect. You are no worse off than before or than you could have anticipated when buying your Railcard.
I'd have a lot more sympathy with your case if the 09:27 had previously been the 09:30, for instance. But that's just not the case - it's a brand new service.
Really? Will the average person be sufficiently well versed in the terms and conditions of their Railcard that they'll know the reason why the fare for the 09:27 is higher is because of the Railcard cutoff? And what percentage of overall passengers use a Two Together Railcard?
I think you are taking the fact that you're annoyed and extrapolating that to everyone else. I get it, it's annoying to have to pay a bit more for the sake of 3 minutes. But that's life; there will always have to be a cut-off somewhere.
they should be doing everything possible to get them on board these new services
They will likely be introducing Advance tickets that make it cheaper to use these services than later TfW ones. But as previously discussed, the aim isn't really to build up patronage; it's to make GUT go away. The DfT doesn't really care whether the new services are well patronised as they no doubt intend to withdraw them as soon as GUT have given up.
If GWR are only running a service every 2 hours, then very strong case for an easement.
If that were the only service from Carmarthen to Swansea, then perhaps I'd see a bit of merit in that argument. But it's not; later services provide connections into other GWR services towards London. Of course people prefer direct services, but there are analogous situations all over the country and yet there are no easements whatsoever to the 09:30 rule for Two Together Railcards.
There are lots of easements where next service is lot earlier than after 11am
Not for the Two Together Railcard!