Agree with this. In administrative law (the principles of which apply here) certain words have technical interpretations that are very different from the colloquial meaning. "Shall" is one of those words - and I too would interpret this as an obligation.
But it doesn't say that "Congress shall promote the progress..." it says "Congress shall have the power to promote the progress..."
If the framers wanted to require that Congress do this stuff, why insert "have the power to" unnecessarily? There's no need for that phrase.
As another point against this being an obligation, if you look at the list of enumerated powers[0], you'll see some that are clearly not obligations. Congress doesn't have to borrow money. They don't have to maintain a navy. They didn't have to establish post offices. They didn't have to create a federal court system. (Granted, it makes a lot of sense for them to do many of these things, but it feels wrong to think that they're required to.)
This area of law is very tricky. As I've stated above, the technical (i.e., legal) interpretation can be quite different from how a layperson would understand the same words.
The basic idea here is that an authority (e.g., Congress) that has been given a specific power (e.g., declaring war) is obligated to exercise that power where appropriate.
Do note the specific phrasing above: if there is a situation in which exercising that power is the appropriate course of action, then that power must be exercised. The authority cannot choose not to exercise the power in such a situation.
So, Congress doesn't have to declare war for the sake of declaring war. However, if there is an existential military threat to the USA (e.g., aggression by the Japanese Empire in WW2) you could argue that Congress is obligated to declare war, as this would be an appropriate situation to exercise that power.
Of course, the above explanation is very simplistic. There can be specific wordings that clarify how much discretion that authority has; there may be case law pertinent to that area; and whether a given situation mandates "appropriate" exercise of a given power is never a black-and-white decision.
That cuts both ways, though. It would be pretty easy to argue that it is not the "appropriate course of action" to implement the copyright or patent system in the way we have, and that, indeed, the "appropriate course of action" is to have minimal -- or even no -- protections.
That's not the reading I'm arguing for. The reading I'm arguing for is that it requires Congress to declare war when it is appropriate for Congress to do so
