«فَلَوْ شَاءَ لَهَدَاكُمْ أَجْمَعِينَ»
Had He willed, He would have guided all of you.
This does not present divine willing as one contingent human cause among other mechanisms. The relationship between the supposition and the specified result must be understood in its own context.
It is unwarranted to infer a universal proposition about every possible mode of guidance or every aspect of divine willing from the conditional particle alone. The specified object of the conditional and the surrounding discourse matter.