[Compare to ME where Alexandrian tactics are used and they never make peace with one another.]
Now, if the Sunnis had won, hundreds of thousands of non-Sunnis would probably lie in mass graves. So it’s possible to rationalize some of the draconian things he is doing now - he is fighting for the lives of the Alawites who, unlike him, can’t leave in the event of defeat. But the likelihood is that absent the possibility of outside intervention, if he had done a Hama-style massacre in every locale he pacified, Syria would be at peace today. Even though that fell far short of Alexander’s massacre of every male inhabitant, it brought decades of peace from Islamist radicals.
https://en.wikipedia.org/wiki/1982_Hama_massacre
But he’s not at liberty to do this today, given the possibility of Western intervention.
You ignore the Vietnam example, but I think it important.
Japan is another good example: they still cannot be forgiven after 4 generations for their behavior pre WW2 by China and NK.
There’s a long term price to be paid for “Alexandrian tactics”.
The key is whether one most needs a lot of enemy deaths now, or to turn the enemy into friends in the future.
Alexsandrian tactics have historically predominated in the ME. Tday everyone hates each other. And for good reason!
Time is the key.