A global medical device manufacturer is implementing SAP S/4HANA Cloud Public Edition. They have a complex pricing structure that includes country-specific government rebates, volume-based discounts for hospital chains, and promotional pricing for new product launches. The pricing strategy must also accommodate foreign exchange rate fluctuations for cross-border sales between their entities in North America, the EU, and APAC. The implementation team has discovered that the standard pricing procedures do not fully cover the requirement for dynamic, multi-layered rebate calculations that are subject to approval workflows before being applied. A junior consultant suggests extensive custom logic via in-app extensibility. The lead architect is concerned about future upgrade compatibility and maintenance overhead with this approach. Which solution represents the most robust and sustainable strategy to meet these complex pricing and rebate requirements within the SAP S/4HANA Cloud Public Edition framework?