“al hakol” clearly doesn’t mean every single person, as chaz say kol hamerachem al ha’achzari, etc, and again the halacha of ain mefakchin
Notice how the rambam here omits the afilu akum, whereas by tzedaka he says it – must be because of darchei sholom exclusively! That by akum there’s a special reason to give tzedaka erc, irrespective of the other reasons that apply to ger toshav or avadim – and that’s darchei sholom. Your quote is a very clear diyuk – shkoyach for the proof!
If the rambam meant the idea of chesed, or emulating hashem as applying to akum, he would have said afilu akum in hilchos avadim, or at the very least said darchei sholom( if darchei sholom means the pshat you’re saying it means) by avadim too