The Salesforce Integration Architect credential is designed for those who assess the architecture environment and requirements and design sound and scalable technical solutions on the Salesforce Platform that meet end-to-end integration requirements.
Certified Platform Developer I developers understand how to develop and deploy custom business logic and custom interfaces using the programmatic capabilities of the Lightning Platform. They know when to use declarative versus programmatic methods, and can extend the Lightning Platform using Apex and Visualforce.
The Salesforce Platform Developer II (PDII) credential is designed for those who have the skills and experience in advanced programmatic capabilities of the Salesforce Platform and data modeling to develop complex business logic and interfaces.
System Architects focus on off-platform systems, integration, securing access between systems as well as managing governance and testing capabilities for deployment and ongoing Salesforce modification requirements.