Dude. No one will stop anyone from being interviewed for an appointment. The most a politican could do to 'put his thumb on the scale' would be to submit his nephew as his primary nominee. Doesn't mean he'll get in. Doesn't mean another candidate won't be considered. Congressional nominations were originally a way to assure that every state would be represented at the Academies, not just the home states of whoever was Secretary of War/the Navy at the time. It's essentially harmless and serves a purpose, so why not? Your suspicions of patronage and corruption are unfounded.