If we add another metric into our decision-making - the percentage of users that have already downloaded the app and stagnating user growth (realistically, it has slowed down since most of people have already either ordered a take out or decided they never will), it doesn’t make sense to add resources into improving a UX that wouldn’t even grow.

Generally I agree with you, but when we focus on specific business use case, it’s harder to convince the stakeholders to work on projects that obviously have lower user engagement.