I use Cardiff Central frequently and think announcements for arriving trains are definitely needed. Terminating trains need to be checked and leave the platforms in good time, especially on 3/4 and the Valleys platforms. If you have a train turn up with no announcements, people do try to get on it!
The problem at Cardiff is how many generic messages they have over their PA. There is one about smoking, unattended luggage and ‘see it say it sorted’ that are probably needed, then you have ‘there are ticket buying facilities at this station...’, ‘this platform slopes towards the track’, ‘due to essential engineering works...’, ‘Penalty fares now apply across the Great Western Railway Network...’ an occasionally very long specific engineering works ones too, which take up quite a lot of time in two languages. Some of these could probably be discarded.
I think announcements queue for 30 seconds at Cardiff and then are wiped off. I’ve also never heard any announcements for any trains ever on the concourse except for platform alterations, pretty sure it’s just generic safety messages only?
I have noticed the delay/cancellation announcements too at Cardiff, I think Transport for Wales must’ve silenced them as they definitely used to play under Arriva. Are they hoping people won’t notice them as much? I think it’s pretty poor to get no info about a cancelled or heavily delayed train.