KWED
Scratching head, scratching knee
Firstly, so you admit that Muhammad was ordered by Allah to cause a great slaughter.Decimated is a translation but it means killed a lot of them, a huge slaughter, its the same word used in the verse:
مَا كَانَ لِنَبِيٍّ أَنْ يَكُونَ لَهُ أَسْرَىٰ حَتَّىٰ يُثْخِنَ فِي الْأَرْضِ ۚ تُرِيدُونَ عَرَضَ الدُّنْيَا وَاللَّهُ يُرِيدُ الْآخِرَةَ ۗ وَاللَّهُ عَزِيزٌ حَكِيمٌ | A prophet may not take captives until he has thoroughly decimated [the enemy] in the land. You desire the transitory gains of this world, while Allah desires [for you] [the reward of] the Hereafter, and Allah is all-mighty, all-wise. | Al-Anfaal : 67
The tafsir explaining the word "يُثْخِنَ" translated as decimated means a huge amount of killing and defeating them (both is implied) and overtaken them, the tafsir explains the word:
يكثر القتل ويبالغ فيه حتى يذل الكفر ويقلّ حزبه ويعزّ الإِسلام ويستولي أهله من أثخنه المرض إذا أثقله
Start with the implication a lot of killing and then other things such as overcoming them and that they are defeated and belittled and Islam is strengthen over them (total victory is implied), but it cannot be without a huge amount of killing.
This is why I am saying the small tribe thing who betrayed Rasool (s) contradicts this verse. He cannot take them as captives, any of them, per this verse.
In both the verses in Surah Mohammad (s) and this one, the same word appears, but there is no direct translation. But it includes huge slaughter and totally overcoming the enemy.
Second, executing several hundred people is the definition of a great slaughter.
In your determination to prove some point (that escapes me), you are admitting to things you have previously denied, ie. Muhammad engaging in unnecessary killing and slavery.