One has to understand that everyone learns systems in a different way. I don't disagree with you in any point. I like the FCOMs, I have learned them, it suits me that they are always the same, whatever type you transition to. I doubt that you will get your information in a dark cockpit in an emergency in a second market's book. btw some operators don't allow you to. So, instead of having to carry two books, carry one! But everyone has his own way.
Happy Landings,
Dani