Trying to create freight capacity elsewhere makes more sense because it probably doesn't put the FOC at too much of a commercial disadvantage, and may actually put them at a slight advantage overall when considering performance and spread of slot opportunities through the day. The idea of bypassing the passenger trains is a much harder sell from a stakeholder perspective because people want long-distance trains to stop in their town, and nobody wants a worse service than at present on any kind of scale.
HS2 services are going to run into this problem in a big way when it comes to the interactions between their trains and the existing service at Rugeley Trent Valley (Colwich Jn), Stone, Stafford, Stoke-on-Trent and Crewe, and no doubt a few other places with lots of interactions like Preston and Carlisle. At least in their case there's time to try and do something about that and clarify how what's left of HS2 can interact with freight and existing passenger services.