Kay Adams: “Saints are still my team. Don’t sleep on them!”

TribuneUK said
If the late season results had been such a strong endorsement of our team improving on O down the final stretch, why did we then can most of the offensive staff in the off-season?

This from your post might be an answer to your question.

TribuneUK said
...5-7 coming into that final stretch. And in those first 12 games, our offense looked, for the most part, seriously subpar.

It's possible that there was an improvement in the offense, DA recognized it, but still decided after the season was over that the first 12 games and last season warranted changes to the offensive staff.

The late season improvement was a combination of better offensive play and the quality of opponents. It wasn't one or the other, it was both.