I see your architecture highly exposed to vendor lock-in. Also, your operations cost could become non-competive since you lack leverage to negotiate (b/c vendor lock-in). Finally, it seems hard to monitor and maintain.
That's right! However, what are the chances of AWS severely increasing fees or shutting down one of those services? Pretty low I guess. Due to Lambda pricing, computing costs are insignificant, and not having to worry about high availability, peak loads, etc., is a priceless advantage.