SFRA customization vs Magento module system, what’s the ceiling on each?

SFRA provides a B2C storefront architecture that can be extended through its supported cartridge approach. It is one Salesforce storefront path, with other approaches to assess separately. Magento Open Source and Adobe Commerce PaaS permit PHP application customization; Adobe SaaS uses another extensibility model. Locate the business rule in the storefront, commerce engine or external system, then prove the supported implementation. More source access does not remove upgrade testing, and an extensible storefront is not unlimited backend control.

Official references: Salesforce SFRA customization; Salesforce storefront developments; Adobe extensibility models.