Since the word agile has become so loaded, you can instead explain why a waterfall practice is linked to predictable problems and avoid buzzwords entirely:
It takes 6 months to act on customer feedback with our current release strategy, and a full year to fix the bugs related to that feedback. We should be rapidly iterating on feedback quickly to avoid churn. Let's try xyz...
It takes 6 months to act on customer feedback with our current release strategy, and a full year to fix the bugs related to that feedback. We should be rapidly iterating on feedback quickly to avoid churn. Let's try xyz...