When the constitution was drafted, time delays necessitated that the military and the President act autonomously for the most part. Congress couldn't convene rapidly enough to expect them to have much say in all but the largest and most drawn out conflicts.
The War Powers Act is codifying this implicit power. The framers never considered a situation where the President and Congress is watching a conflict play out across the world in real-time and making decisions. So it's literally impossible to say how they wanted this to be handled. That's why they gave Congress the powers to write laws.
If the president actually has the authority to send troops into combat without a declaration of war, then Congress can’t take it away from him, just like Congress can’t make it illegal to veto bills.
The War Powers Act doesn’t really set any punishment for the president if he ignores it. It effectively says that if the president does certain things (consult with Congress, follow certain timelines, issue reports) then Congress won’t complain. Presidents have generally followed those procedures without admitting that’s what they’re doing (they issue reports “consistent with” the Act, but never admit the report was required by the Act). But if a president completely ignores those requirements, Congress has to figure out what to do about it; which is exactly what would happen if the Act didn’t exist.
