but rather, was refusing to accept that the scenario they're talking through with you would ever involve an effectively deployed cut-through switch (since that's basically never).

Nope, the argument was exactly if a cut-through switch exists or ever existed

Edit: Actually the conversation came back to me:

He asked me about the frame format. Once I drew that on the board, he asked why is the DST before the SRC. My answer was in order for the switch to start doing the lookups ASAP and that's when I mentioned that a cut-through switch can switch the packet before it even finishes receiving it.

After that we spend the rest of the interview time arguing if cut-through switches actually exist or not. Both he and I having too big of an ego to let it go..