No one disputes that the President is CIC. However, the "recognition" of the constitutionality of legislation is a function reserved entirely to the courts, not the President. If legislation of any kind is passed into law, over his signature or over his veto, it doesn't matter what he thinks of it -- he is obliged to abide by it or refer it to the court. IOW, he is not supposed to be a law unto himself, he is only empowered to "faithfully execute" the law -- though that fact will not always impress him.
Infrequently, the court will actually do its job and put a stop to presidential excess, for example, when it stopped Truman from seizing the steel mills during Korea. I note that Johnson was very careful to get authorization from Congress for his action in Vietnam. Bush also took great care to obtain Congressional authority for his current war on terrorism. And similarly, his father did so before embarking on his Desert Storm campaign. Aside from the obvious issue of appropriations, it's often, though not always, politically expedient to do so.
The original wording of the war clause gave Congress the exclusive power to "make" war. This, however, was revised to "declare" in subsequent drafts when they realized that the President might have to repell a sudden attack or urgently pre-empt foreign encroachment before Congress could convene and decide. They never intended that one individual, acting on his own, should have the power to commit the country to full-scale war. They had seen this sort of thing done in Europe between rival royal families and would have none of it. It's all in Madison's 1787 notes (in fact, he's the one who proposed the change in wording.) By imposing a time limitation, the War Powers Resolution merely re-elaborates this principle, that the executive must be allowed some degree of flexibility but the ultimate decision to go to war rests with Congress.
"... that the President can act with something called 'specific statutory authorization,' whatever that means."
It means the same thing it did in 1798 and 1799, when Congress, unwilling to declare war on France, nonetheless gave Adams the go-ahead to engage in continuing hostilities with them. They enacted at least a dozen statutes to this end. The War Powers Resolution, if challenged, will do just fine -- if Congress has the intestinal fortitude to defend it, that is.
"...the explosion of federal agencies over the last 70 years, all of which have been created at the behest of Congress..."
Certainly with their collusion, and at times, their meek acquiescence. No question about it -- Congress has willingly abdicated much of its own power.
And I agree with you absolutely that states' rights have taken a terrific beating, and the commerce clause is grossly misconstued and misapplied.
Anyway, you're obviously up on the history - how about the law? There was a really interesting article in the Columbia Law Review about 15 years ago entitled "Suppose Congress Wanted a War Powers Act That Worked" - essentially, IIRC, it argued that the fatal flaw in the current WPR was the failure to account for the possibility that executives would just ignore the thing, and explores possibilities for repairing it. And if you want a hint about the current court, Justice Breyer had an article in the Georgetown Law Review way back in 1984 that was rather skeptical of the appropriateness of such legislative vetoes, and instead proposed some substantive alternatives. Not that such a thing would stop him from ruling against a Republican president, of course ;)