speaker is someone that normally fights demons, but fell for a trap set up by A, a human. Speaker has always hated A.
私としたことが……相手が、魔族じゃないと……Aごときと侮って、視野が狭くなってた…… pass out
I, of all people.... A...isn't a demon....underestimating (someone) like A, I became conceited.
from what i can tell ~と侮る seems common as ~を侮る
from 「たかが過換気」と侮ってはいけない, i assume that this is used as a quote to describe the preceeding claused just like "ミユキちゃんが結婚した"と知ってる
are both 相手が、魔族じゃないと and Aごときと attached to 侮って or is it 「相手が、魔族じゃないと……Aごとき」と侮って?
more generally
If a random sentence had ~を侮る instead of ~と侮る, i probably wouldn't bat an eye. I suppose i could say the same for ~と知る vs ~を知る. CTRL-F'ing my past texts i found を知る is used 5x more often than と知る。
After this encountering this ~と侮る sentence i realized i really can't tell the difference between ~と知る vs ~を知る either.
Thank you for any clarifications.