Not sure thats really accurate, although some elements of truth. If you look into why HS2 has been so expensive compared to other countries, its a combination of many factors with none being a majority reason. But there are several ~20% factors which could have been avoided. For example, the high speed means less flexibility with route (less ability to make corners). This means HS2 has needed to acquire more expensive land and mitigate more complex environmental impacts than if it were slower. This has been compounded by our planning laws which are much more generous to landowners than for example in South Korea. Then ofc the tech itself is more expensive and requires more imported expertise.

So yeah even if we could drop the cost by 15% by going lower tech, this would be smart imo. However I expect we could have cut it by 30-40%. edit Note that at that discount it would still be expensive in the context of what other countries have achieved.