The technical differences between UI5 Controls and UI5 Web Components are described in this blog post: https://community.sap.com/t5/technology-blogs-by-members/ui5-controls-vs-ui5-web-components-technical-differences/ba-p/13775950
Besides those technical differences, there are other aspects that differentiate both technologies to choose the best option:
PerformanceMultiple JavaScript frameworksOne set of Web Components
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