Regarding "Thus, there must be absolutely 0 residents already capable of performing the job.", I think on paper it's true but the burden on the employer to prove that there are absolutely 0 residents already capable of performing the job is really low: https://www.law.cornell.edu/cfr/text/20/656.17
(e)(1)(i) Mandatory steps. Two of the steps, a job order and two print advertisements, are mandatory for all applications involving professional occupations, except applications for college or university teachers selected in a competitive selection and recruitment process as provided in ยง 656.18. The mandatory recruitment steps must be conducted at least 30 days, but no more than 180 days, before the filing of the application.
(A) Job order. [...]
(B) Advertisements in newspaper or professional journals. [...]
(e)(1)(ii) Additional recruitment steps. The employer must select three additional recruitment steps from the alternatives listed in paragraphs (e)(1)(ii)(A)-(J) of this section. Only one of the additional steps may consist solely of activity that took place within 30 days of the filing of the application. None of the steps may have taken place more than 180 days prior to filing the application.
(A) Job fairs. [...]
(B) Employer's Web site. [...]
(C) Job search Web site other than the employer's. [...]
(D) On-campus recruiting. [...]
(E) Trade or professional organizations. [...]
(F) Private employment firms. [...]
(G) Employee referral program with incentives. [...]
(H) Campus placement offices. [...]
(I) Local and ethnic newspapers. [...]
(J) Radio and television advertisements. [...]