Surely the point is that there are only goi g to be 2 tph from London to anywhere long-distance GWR so they are going to be crammed with people travelling through to South Wales & the Southwest, (and changing off the S Wales for Bristol via Bath). That latter fact would mean that only the Penzance services have a chance of having capacity. Just imagine the EUS - Reading loadings if there is just one fast per hour. Agree, however, that its tough on anyone starting at Reading and heading for Cornwall.That’s because commuters became savvy to that. Its unlikely many people will be able to work it out given these closures are a rare occurrence.
Trains to Penzance/Plymouth are pretty much hourly from Paddington on weekends so why would an hourly service from Euston be any more busy compared to those from Paddington?
I was hoping to follow the exact route but didn't really manage; might have been more informative in daylight