The "FE as cruise pilot" concept is now obsolete. . . but it was at one time used by the world's most major airlines during that time of transition years ago.
I have been around this gig for more than a few years. And I was a PFE "years ago." Other than the very limited case at QF, I have never heard of this. Most of the major airlines have used second officers since ALPA tried to force the third pilot issue during the time of transition you are talking about which came as the 737 entered service; so I am not sure what PFE-as-a-cruise-pilot concept you are talking about.
There are some highly qualified FEs who for one political reason or another are on the PFE track. There is no doubt that they can do the job; and many have. But by and large, they realized that they were the ones who needed to get off their duff and get their ratings. They did so and bid into the front seat. Human nature being what it is, there are some who just sat there, feeling like the company owed them something just because of a few words on a piece of paper. At this stage of the game, with a few exceptions, those who are left are generally thought to be in the latter category.
Enter the Atlas purchase of Polar and some creative asset transferring to cloud the picture and "shazbat" they get an arbitrator to buy off on their scope clause and the "awww poor me" game.
The PFEs knew this was coming years ago. They could have gotten their ratings and been ready. Instead they want the company to pay them to sit? Or they want to impact a whole bunch of pilots, even for two weeks, while the company fires and re-hires to adjust the seniority list. Or they want the company to pay for the training they should have gotten for themselves?
I guess it is much easier to sit back and blame the Atlas pilots or the company for all their troubles. But that's human nature I suppose.