The quality of online wellness communities is difficult to explain using simple growth metrics. However, an empirical understanding of the structural and relational factors that define quality has proven elusive. To fill this gap, we analyzed over 17 million posts from 56 Reddit wellness communities between 2023 and 2024 by applying the sociability-usability framework, measuring user-based factors (e.g., User Retention, Gini Coefficient) and content-based factors (e.g., Interactivity, Quasi-Quality Index), while also examining the impact of identity (Linguistic Distinctiveness and Topic Drift). Our analysis confirmed that quality depends on a stable core user base and meaningful reciprocal exchanges rather than conversation volume. A strong identity creates a trade-off, enhancing internal cohesion while acting as a barrier to new user inflows. Overall, we challenge the conventional ‘growth=success’ paradigm, establishing structural sustainability as the core mechanism for defining quality in online wellness communities and offering a new framework for their design and evaluation.