This seems incorrect
> cases in which the Executive possesses a constitutional or legal discretion
In this case though the laws wording would determine where the discretion starts and ends. "... whenever he shall find as a fact that such country—" so the president is limited by a.1 and a.2[1], the president was only granted discretion in under those proscribed limits.
So a find that says ~"neither a.1 or a.2 is occurring therefore I impose a tariff as president"(claiming no conditions to impose a tariff under the law are met but declaring a tariff anyway) seems reviewable by the court from your sources. Only having a finding is not enough, the finding has to follow the limits of discretion put forth by the law in question.
[1] https://www.law.cornell.edu/uscode/text/19/1338
edit to remove double negative