You are right in what you say Station Master. A work college was a driver based at Old Oak Common in the "Freight Link" and he was in the initial batch of drivers who learned the new type 5's The key that made the whole 59 project as you say was the second to non support EMD offered. He has told it was quite common to find EMD engineers at Old Oak or Acton or even riding out on the type in traffic and discussing any issues that he would be having with the loco's. The fault books would be constantly checked daily and the exam program that locomotives had was also brilliant. During his time on the 59s he only ever had to protect his train once near Taplow when he was working 4,000 ton loaded train and the alternator gave up the ghost and and he could apply any power. A new class 60 came out to rescue him and drag the whole lot back to Acton and even with a dead loco and 4,000 tons of stone the 60 manged very well.
With regard to class 66s having spent the best part of 15 years working with them they are the cooking version of a class 59. However, the diagrams these locomotives work are far more punishing then any diagrams the former BR trainload companies ever created. The loco's mile per causality rate is streets ahead of what class 37s, 47s, 56s, 58s and 60s would ever achieve. Admittedly some of the operators who operate the class 66s have totally flogged the loco's and they are in need of major exams but on the whole what one of these locomotives can do on a full tank diesel is amazing. Yeah they can be rough riding and they are loud in the cab (but so are the 59s) but they are a solid loco and says something when GB want more of them and have paid a premium to get them.