I see your point but, if you use this service this way you are probably misguided to start. The best use of this service is to kick start growth from 0 to >0 or to test new market segments. I would think spending >LTV is okay* because you are just experimenting and you are paying for the knowledge. Or, you may plan to build some organic traction off of this initial bump in users so long-term the greater expense makes sense.

This service will help you grow, learn, and fail fast and cheaply if needed. It probably shouldn't be your main user acquisition pipeline.

*Also, you might not even have a LTV yet because you have 0 users.