With the resources we have available, I try to do some of each. FWIW, I just tried a couple of my older MRE’s in the last few days, and they were still fine. Long term stability is one of their strengths, although menu boredom can be a drawback. That’s why I try to keep a decent variety of “makings” in the pantry as well.
Menu boredom is overrated.
Some people are on really restricted diets and you do get used to it. Not saying it's easy, but it's possible.
You can learn to be grateful for what you DO have to eat instead of complaining about not having variety.
And in some places in the world, they eat pretty much the same thing day after day because they don't have anything else.
One thing I rarely see mentioned in the prep lists is good quality multi-vitamins.
If you are stuff on a limited diet, it is very likely not nutritionally balanced and there's a good possibility that it will be deficient in some vitamin or another.
There's no sense in dealing with scurvy (Vitamin C) or (God forbid) night blindness when you need to be able to defend at night.
Mineral supplements are also important.
There's no point in succumbing to an illness or infection because you are physically compromised from a deficiency of some kind.