As to the other part about the を見返る maybe it’s a usage related to this question:
Maybe it’s just something that has become a natural collocation even though it appears to be an exception to the normal rules?
Edit to add:
I missed this from one of the HiNative threads you posted:
見返すand 見返る mean look back. 見返る is old-fashioned and we use 振り返る instead. Only 見返す means look once more
From that bolded part, maybe the phrase is just an old fashioned equivalent of 過去を振り返る?