I don't really get the New Street argument - if something goes wrong, they just shift trains on to other lines (I.e. Nuneaton). Contrast that with Clapham Junction, whereby if that goes down you basically have no trains going in to either Waterloo or Victoria, two of the busiest stations in the UK.
The reason I say New Street is simple. If Clapham Goes down, it only really affects the south east. I’ve had a look at some reactionary delay data and the sheer amount of disruption that is caused nationwide is unbelievable. Say I breakdown in the tunnels at New St towards Grand Jn. Straight away, that’s screws up the pattern into Euston, because my TM may be needing to go to Manchester, the Pwllheli at International may then get held there, which on a service that only runs every 2 hrs could be a total pain for someone over a 100 miles away. The XC that’s possibly already running late will now get held up going south and get in the way of a GWR at Reading, that then causes knock ons into Paddington and back out to Cornwall or South Wales. Meanwhile, the family wanting to go to Walsall can’t because they’re stuck waiting for a path out the other way, and the LM that’s had to go through the Derby Tunnels towards London, has then held up various freights trying to get to Ipswich which will then disrupt a Greater Anglia service or 4! Meanwhile a delay at Clapham has meant a lot of harrumphing by Giles because his train to the south coast has just changed to the next platform.