So you think it would have been better with no input from Congress? The President has the authority to make this executive agreement on his own. At least now Congress has some input.
Absolutely.
In the current scenario Congress has givven the POTUS agreement the force and legitimacy of US Law. A future POTUS cannot nullify it "with a phone and a pen".
If Congress instead had forced POTUS to do this only under "Executive Agreement", the next POTUS could simply decide it's no longer in force and stop abiding. Sanctions and all would be back in force a mere 18 months from now.
As it stands it will take an act of Congress to stop this, and a VERY high threshold of 2/3 of both Houses.
But Obama needed to show he had the Congress with him or Iran would not negotiate.
Thus "Fast Track Nuclear Treaty" was invented.
This method for International Arms "Treay" has never before been even tried.
Now it's the Law of The Land.