If you use Spring Boot you don't gain some of the features in Grails that make development much easier. I would give Grails another try. The 3.x codebase has gotten much more stable. Spring Boot is just a part of the many parts of Grails. In my book I share some of the components that are included in the overall Grails architecture.
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Building a Better World in your Backyard by Paul Wheaton and Shawn Klassen-Koop