> the fact that somebody is paying for said app implies that it is useful.

False. This is a tautology, aka circular reasoning.

For example purchasing and consuming heroin does not add value to anyone's life.

A lot of social media consumption (eg. TikTok) doesn't improve one's life, yet people consume them out of addiction.

Someone choosing to do something doesn't mean that it is valuable for them. Another counterpoint would be suicide.