[The Philippines has never shown the ability to successfully go scorched earth on the insurgents.]
This is not rocket science. Even the most incompetent regimes can exterminate entire regions. It’s basically a large-scale hunt, where every living human is killed. Alexander was able to do this with fairly primitive weaponry. The Indonesians did it mostly with edged weapons not too dissimilar from what the Greeks used. The Hutus killed 800,000 using similar methods.
https://en.wikipedia.org/wiki/Rwandan_genocide
You can keep saying it’s possible but it’s not probable or possible for the Philippines armed forces, especially without American support.
Further, Duterte has not stopped the drug trade or the drug problem, regardless of the public shows of killings early on.