Is not the statement that there is a minor shirk (polytheism) and a major shirk, and distinguishing that in actions where shirk or kufr (disbelief) were mentioned without detail, a watering down of the religion? And what should be done about that?

Dividing disbelief (kufr) into major and minor is derived from Islamic law, and the ruling on it is derived from the evidence. No one has the right to accuse someone who holds a valid opinion in Sharia, or to castigate those who differ. The fact that abandoning prayer is minor disbelief does not mean it is trivial; rather, it is greater than the major sins. Superstitious omens (al-ṭiyarah) have details: some are major disbelief, and some are minor disbelief. During admonition, texts can be left without interpretation to work their effect on the hearts. Those who are negligent must be advised and warned of Allah's punishment.