~10 years ago, there was a general inclination in the app ecosystem to build models for predicting user-level monetization and engagement. These predictions, often related to user LTV, would then be "rolled up" into aggregates for things like ROAS calculation.
With the benefit of hindsight, this approach was mostly a dead end. The data that feeds these models has too much variance, and the decisions that these models are used to inform (marketing adjustments, product changes) generally aren't scoped to individual users, anyway.
The modern approach that I see commonly implemented is to use cohort analytics for these kinds of decisions at the top of the funnel (marketing) and to intervene with specific users in ways that relate to group membership. This tends to smooth out the impact of outliers and results in less overfitting and more reliable results, although it also necessarily assumes that changes in product and marketing are moderate.