I am glad that you have thought through this.
The verse that you quoted DOES NOT say that “sabbe sankhara LEAD TO dukkha.”
It just says, “sabbe sankhara dukkha” OR “All sankhara are suffering.”
So, “kusala-mula paccaya sankhara” are the types of sankhara that DO NOT lead to suffering. But one still has to strive to attain Nibbana. There is an EFFORT involved.
1. Those Paticca Samuppada (PS) cycles that lead to suffering ALWAYS start with “avijja paccaya sankhara.”
– Those sankhara that lead to suffering are defined in the Paṭiccasamuppāda Vibhaṅga: “Tattha katame avijjā paccayā saṅkhārā? Puññābhisaṅkhāro, apuññābhisaṅkhāro, āneñjābhisaṅkhāro, kāyasaṅkhāro, vacīsaṅkhāro, cittasaṅkhāro“.
Translated: “What is avijjā paccayā saṅkhārā? Puññābhisaṅkhāra, apuññābhisaṅkhāra, āneñjābhisaṅkhāra, kāyasaṅkhāra, vacīsaṅkhāra, cittasaṅkhāra“.
– See #14 in the post: “Vacī Saṅkhāra – Saṅkappa (Conscious Thoughts) and Vācā (Speech)”
2. Those PS cycles that lead to the end of suffering start with “akusala-mula paccaya sankhara.”
– These types of sankhara DO NOT belong to the above kinds.
– See, “Kusala-Mula Paticca Samuppada”
As I explained in my previous comment above, the difference between punnabhisankhara that LEAD TO rebirth (in good realms) and those that LEAD TO Nibbana is one’s comprehension of anicca, dukkha, anatta (or the Four Noble Truths or Paticca Samuppada.)
– Punnabhisankhara become “kusala-mula sankhara” with the comprehension of anicca, dukkha, anatta.
All posts on Paticca Samuppada at: “Paticca Samuppāda“