I'm a bit late to the party, but let me try to dissuade this brain-in-a-jar philosophy.
The biggest problem I can see with Solipsism is that, for reasons similar to what you covered, whether the universe exists independently or not it functions exactly the same as if it were independent and physical. To any external observer they would be indistinguishable... so while possible there's little point in considering the brain-in-a-jar scenario as it changes nothing about how we discover the universe we are living within.
Exactly what I was trying to say!
I like philosophy, but I don't know the history nor do I care all too much. I just want to know how the lightbulb works, not the half-baked theories that lead to it. For example, I have no reason to know that a few hundred years ago they believed in four bodily humors. It wouldn't help me diagnose or treat a patient with cancer.
Although... there is also the problem that this outside construct is not defined. Simply saying that "I can't know for sure how my consciousness gathers information, for it could all be an illusion" just pushes the problem back. If we continue to put possibilities on the table, we could disprove them by the artifacts each would generate. A fleeting dream of a butterfly, for example, would be limited by the purely physical limitations of a butterfly's brain.