Very interesting in general, but I thought that officers' commissions came from congress, but warrant officers' commissions came directly from the president.
U.S.C. Title 10 Subtitle A-General Military Law, Part 1-Organization and General Military Powers have the statutes specific to the authority to appoint commissioned officers in the military services. Appointment of officers in the commissioned grades is made by the president with authority to appoint delegated to each service secretary. See sections 64, 12203, 12213, 12214 and others.
Subtitle E, Part II, chapter 1207, section 12241 Appointments of warrant officer is made by the pleasure of the secretary concerned.
I think you are confusing process for attending the military service academies that have a Congressional nomination admission process.