Even though two years has pasted, it is still the cause it is the GWML Mainline. The comment is very much still in date. As shown by these two photos GWR still makes use of those lines = https://flic.kr/p/2qNiA1P https://flic.kr/p/2qNiFTK  The link for the doc has been replaced by this link, due to it gets updated every 3 months for safety reasons. This is the most recent one which is the December 2024 issue. https://sacuksprodnrdigital0001.blob.core.windows.net/sectional-appendix/Sectional%20Appendix%20full%20PDFs%20December%2024/Western%20and%20Wales%20Sectional%20Appendix%20December%202024.pdf
It can also be found hear under the Western Sectional Appendix = https://www.networkrail.co.uk/industry-and-commercial/information-for-operators/national-electronic-sectional-appendix/