I understand the motivation behind your comment but that highlights one of the things that is inherently wrong with the "debates’. It is virtually impossible to be able to provide a comprehensive answer to any complex issue with the current format. What you get are soundbites and slogans and no substantive discussion/debate.
What would be a better format and in some ways borrows from your suggestion would be to have a certain number of topics that the two candidates could actually discuss. Maybe have each candidate give an opening address of 2 minutes and then two alternate 5 minute periods where each candidate articulates their agenda on the topic and end each period where each candidate gets the opportunity to ask the other a question where the candidate has up to 2 minutes to answer. For the next topic, the candidates swap positions etc.
And before it starts the two candidates are told they any diverging from the topic will result in a first warning from the moderator. Any further infractions the candidate will lose the remaining portion of their time.