That's only a small part of why all content should be able to be unsynced. The other part of it is the *challenge*. Yeah, there's a lot of things that trying to do unsynced is just a faceroll because you outgear it so much, but some things are actually harder *not* because of the damage numbers or whatever, but because of the much lower party size. My friend and I enjoy two-manning content, just trying to push the hardest things we can, and see how far we can go. We do this in many games. There are some things we'll likely never be able to 2 man purely because of how mechanics go, but that doesn't mean we don't like giving it a good try regardless, see if there's any way we can perhaps cheese the mechanic, or maybe somehow skip it entirely.
To this effect, I even think *current* content should be able to be unsynced purely because of that reason: The fun of the challenge, push as hard and as far as you can go.
THIS is why I say more options, not less.