Well, actually no it isn't just now. Predicting the future usage of rail is very hard post-Covid, but I do wonder if building a very high speed line from which freight is excluded by design will turn out to have been a bad move in the long term. Long distance freight is one thing that rail is really efficient at, environmentally speaking. Yes, I know the official answer is that HS2 will take passenger traffic from WCML and make more room for freight, but maybe in forty to fifty years most long distance passenger will go by autonomous car. The railway has survived as long as it has by being adaptable, and HS2 isn't.
Autonomous cars will never match the speeds of rail over long distances and there are environmental concerns regarding the production of batteries and the particulates produced by their tires. Plus this idea would require more roads to be built.
There are services today that don't stop between London and Crewe, York, and Stoke. It makes sense to build a high-speed line to carry these, allowing the existing lines to carry more freight and services which stop more frequently.
I'm also unconvinced that any HS2 opponent would support a freight line. East West Rail is evidence of this - a standard line, partly on an existing alignment, and people are up in arms.
Regarding the suggestions of tunneling the whole of HS2, the tunnels create a lot of emissions during construction so from an emissions perspective it's better to avoid tunnels.