What is the validity of the statement of one who believes in prioritizing human interests over the interests of religion, and that religion is deferred or postponed when they conflict, and does this apply to acts of worship?

The five necessities or universals (religion, life, intellect, progeny, wealth) have been agreed upon by all divine laws for their preservation. Scholars have differed on their order, but most prioritize the preservation of religion. The reason for prioritizing the preservation of religion over others is that its fruit is the happiness of the afterlife, and because the rest of the necessities were intended for its preservation.

The concession for a traveler to break their fast is not a prioritization of human interest over the interest of religion; rather, it is a consideration from religion for the human condition. Breaking the fast with the intention of making it up later is an act in accordance with religion, and it is a تسهيل (facilitation) from Allah for His servants.

As for writing "Salat upon the Prophet (peace be upon him)" on a car, this does not contradict the interest of society. In fact, sending blessings upon the Prophet (peace be upon him) and reminding people of it improves the state of society, due to its virtue and the reminder of the excellent example.