FM is just a nicer name for generalist.
In all fields it is not good to be a generalist. The pay is lower. Demand is lower as well.
But as a generalist it doesn't mean you cannot move on to specialize or go into niche sub sectors. But need to work on it and find those opportunities.
A common example is Aesthetics. But this example has been used to death frankly.
I am not saying it is easy to find a niche market or to specialize on your own. But there are possibilities. From a non procedural point of view, a generalist can educate themselves to have as much knowledge as a specialist. What they lack though is experience.
Having depth in knowledge is good. But if you don't use the knowledge you will lose it. And as a generalist unfortunately you will usually see all the very common things. So you will lose the fringe knowledge. The specialists will keep up cos they see what they are supposed to see. What is a FM supposed to see? Complicated esoteric cases? I don't think so.
From a career perspective it will be very tiring to try to be everything to everyone and yet be totally aware you are not going to replace the specialists anyway.
Disheartening.