I don't understand the commentary in the Civ IV unmodded AI. Like, how many times did you see an unescorted Settler in the base Civ 4 game? Seriously, things as stupid as this aren't accounted for in 5, 6, and now 7 (7 from what I hear). They don't care.
EDIT: And, how about the Civ 3 unmodded game, ever see an unescorted settler without some bizarre situation that caused it? Nope, you didn't.
EDIT 2: That's literally how you beat Deity in Civ 6 -- go find that settler, which doesn't turn into a worker when captured (like V) and create your second city. Is *this* what Civ was supposed to be?