[IRV] will strike out everyone but the top two, then pick the most preferred candidate between the two.

The current system does that just fine.

Mr. Drutman opined that no single-winner election can defend against two-party dominance. I would like to ask him, in that case, why he debated on the side of one voting system over another for such elections.

This seems to be the central issue. If you assume that single-winner election systems will inevitably be two-party dominated, then IRV does basically everything you could want. It will strike out everyone but the top two, then pick the most preferred candidate between the two. In a two party dominated Approval contest, the voters must decide for themselves how much they value influencing the contest between the frontrunners, and how much they value making other distinctions. You'll notice that in two-party dominated elections that use plurality, voters similarly have to make choices about which distinctions they most value making. I think this is why they often compare Approval to plurality and emphasize later no harm - the kinds of elections that IRV advocates worry about look very specifically like Gore losing to Bush in Florida.

When I talk to local IRV advocates, the most persuasive thing I can do is to point out that local races don't look like Bush vs Gore, because when there is a competitive race, it is often because there is an open seat, and 3 or 4 people who have been waiting to run for that seat all see their opportunity.

At the end, someone announced that there would be a place for discussions following up, some organ of Yale's, but I didn't record the name of that organ.

Mr. Drutman opined that no single-winner election can defend against two-party dominance. I would like to ask him, in that case, why he debated on the side of one voting system over another for such elections.

AV, on the other hand, is exaggeratedly simple to understand and write, with no restrictions on the minimum or maximum number of candidates to be evaluated.

On a theoretical level, IRV doesn't seem to me to have good enough sides to beat AV.