Well that may have been the case on passenger side, but the aim was for each 66 to replace 3 locos , which they did and it was goodbye to the 31s,33s, and freight 47s.
The plan IIRc was to retain the heavyweight 37s, 56s, 58s and 60s. Time tells us that didn't quite pan out.
The thing with the three shadowy franchises was that they would never get sold to three competing companies - a tiny slice of a tiny slice wasn't worth bidding for to then have to compete for the tiny slice with others...er...not gonna work.