If I would be the interviewer in this kind of situation, I would just follow up with something like this: "that might be a good option, but let's assume you need to build a tool to replace those excel sheets, ..."
Surprisingly often you do get an interviewee who just won't accept the premise of the hypothetical. I've had people get hung up on the equivalent of 'but I'd just use excel' even with prompting/nudging/explanation that this is an exercise.
