That is how it's been interpreted, it's not actually what the founders had in mind when they wrote the constitution. They wanted congress to be a check on the presidents 'commander in chief' role by reserving the right to declare war for congress.

Agreed, the founding fathers definitely didn't want a king who could wage war at his whim, but unfortunately the constitution as drafted didn't envisage a standing army under the bidding of the President, it expected militias to be levied for defense as required.

It's still technically illegal for the president to do that (which means squat thanks to the SCOTUS) but he can be challenged through the courts for it.

Kinda but not really. Something is only illegal if it is within the powers of the lawmaker to bind in that way. If the constitution doesn't provide that power then it is ultra vires and as if the law didn't exist. Unfortunately the constitutionality of the 1973 act is definitely questionable - I listed more in another response but

https://en.wikipedia.org/wiki/War_Powers_Resolution#Questions_regarding_constitutionality

and

https://en.wikipedia.org/wiki/Campbell_v._Clinton