They may have been cutting edge, but when you are at the forefront of technology you often end up in going down expensive dead ends and failures. Everyone who is waxing lyrical about the Class 60 seems to either forgotten or be unaware of how long it took to get them into traffic and working reliably. BR could afford this lengthy period of bedding in, but there's no way today's freight companies would be that patient. The Class 66s may be crude and less powerful, but they worked pretty well straight from the start without any major problems which couldn't be said about the Class 60.