Is being content with Allah instead of seeking human intercession, after taking all necessary measures and seeking Allah's guidance (istikharah), the essence of reliance upon Allah and more beloved to Him?

There is no harm in seeking an intermediary or an intercessor to help you obtain your right to a certificate or a job. This falls under the category of taking the enjoined means, like the Hadith: "Tie it and then rely [upon Allah]." The one who makes such a good intercession will be rewarded for it, based on the Almighty's saying: (Whoever intercedes with a good intercession will have a share of it), and His (peace and blessings be upon him) saying: "Intercede and you will be rewarded." Leaving intercession, relying solely on Allah, is not arrogance; rather, it may be a sign of perfect reliance [tawakkul]. And whoever relies upon Allah, He is sufficient for him, as in His Almighty's saying: (And whoever relies upon Allah - then He is sufficient for him).