While I did not downvoted it I think it is because:
- the question is not very clear
- This question already has clear answers on this site
- In your question you make false claims. You claim that:
It seems to me there that the most common definition of opportunity cost in economics is that opportunity cost is the net benefit of the next best alternative forgone.
Yet the answer to which you link states:
As other answers clarified, the Opportunity Cost has been defined as the value of the best alternative foregone.
Moreover, your question is basically, is opportunity cost the value of the next best alternative or net benefit, and for support of the definition of net benefit you quote answer that says its the second best alternative and you do not provide any evidence for the net benefit use.
Note if you hover over downvote on a question you get the following pop-up:
This question does not show any research effort; it is unclear or not useful
In your case your question does not show much research effort, you link to older answer and claim it says something it does not say. Also, your question is not very clear since you do not explain where did you get the alternative to the common definition (value of next best alternative).