Does the phrase "Things come to you according to your effort, not according to your desire" contradict creed, even if the intention behind it is to remind one of the necessity of striving for worldly and otherworldly success by the will of Allah?

There is no apparent doctrinal violation in the saying, "Strive, My servant, and I shall strive with you," as long as what is meant are the means by which sustenance is obtained. For Allah has ordained these means: some are acquired through effort and earning, and some are obtained without earning. Effort is of two types: effort to earn sustenance, such as industry, agriculture, and trade, and effort through supplication, reliance [on Allah], and benevolence towards creation.