I'm not sure how a 4tph Rhymney Valley service is meant to flow into a 5tph Barry one at Central. It's bound to look something like:
With the benefit of hearing the slide described in the meeting ...
10 trains an hour arriving Queens Street via Cathays
8 trains an hour arriving Queens Street via Heath
=== 18 trains at Queens Street each way ===
6 of those trains on to Cardiff Bay and so ...
=== 12 trains an hour into Central
2 trains onwards to Radyr via the City Line (and on to Aberdare?)
2 trains onwards to Bridgend via Barry Town
3 trains onwards to Barry Island via Barry Town
4 trains onwards to Penarth
which means I have lost one train / turn around at Central??
So for Central ... (one platform, train there for three minutes, next in 2 minutes behind)
Every 5 minutes, alternate trains arriving from Cathays and Heath - 10 minute service from each of those lines
:02 and :32 arrival from Coryton
:07 and :37 from Treherbert
:12 and :42 from Rhymney
:17 and :47 from Aberdare
:22 and :52 from Caerphilly
:27 and :57 from Merthyr Tydfil
:00 :15 :30 :45 on to Penarth
:05 and :35 on to Radyr (and Aberdare?)
Three of :10, :25, :40 and :55 on to Barry Island
:20 and :50 on to Bridgend
And arrivals into Cardiff Bay (10 minute service), roughly
:02 and :32 from Rhymney
:12 and :42 from Merthyr Tydfil
:22 and :52 from Treherbert
I will refrain from fine timing over junctions and looking at where parallel moves can be made!