I feel your concerns are very logical and I think you are a very logical person which is very good and I’m also like you who likes to go deep into everything , rather than believe just anything on hearsay.
Regarding your question on any planets get exalted or debilitated. When a planet is exalted it is at its best and when it is debilitated it is at its worse condition. When the planet is exalted or debilitated it got entirely to do with its nature and character. For example Sun is exalted in Aries because when the Sun is in the sign of Mars, only with Mars energy it can be at its best. With Mars ability to make it courageous and bold. And only with Venus energy of pleasure and materialistic desires the king loses its authority and command.
By the way I never heard that Sun exaltation is because Mars is his commander in chief , Mars is commander in the hierarchy, but referring it is Sun exaltation is humorous.