The 769's aren't reliable enough to commit to more workings. Valleys lines aren't as busy since covid as commuter traffic hasn't returned to same levels. Don't get me wrong, they are needed, especially on event days, but are coping much better than pre-covid.As crazy as it sounds (erm not so much) two more class 769 diagrams on the Rhymney line would free up two class 150/2s to cover the North Wales duties. To be fair though, the last time I looked, every single Rhymney line diagram except the 769s was only two cars anyway, rather than the multiples seen when 142s and 143s held sway.
It's likely the extra services will be canned and 150's will continue to cover as they are. There's no way 2 more 150's could be freed up to run the extra services. The only other option would be to have a single 153 on the additional limited stop services until the 197's come in.