Agree. "Aston to Acton" is a pointless white elephant. You need Euston to be able to move enough* trains off the south WCML to get any real benefit from Phase 1.
* 9tph if you just use what's there now - three Manchester, three Birmingham, two Liverpool and one Scotland.
Bit in bold - why ?
Euston or its vicinity isn't the final destination for many people who arrive there. Old Oak will have connection to the Elizabeth Line giving a direct link to Central London and the City (better than the Northern Line from Euston by far) as well as a direct link to Heathrow (which Euston can't offer) and if platforms were added to the North London Line and West London Line at Old Oak, you'd have direct access to swathes of North London and South London - again far better than anything Euston can offer.