While I cut my teeth learning Java with Spring Boot, you are beholden to some extent to where Pivotal wants to take it. I've been bitten by their decision before to make a breaking change to an API, forcing a lot of work to bring my app back up-to-date. Quarkus, however, is based on Java/Jakarta EE, which has no single company behind it and a strong history of backwards compatibility. There is no obligation to use all the Quarkus specific elements. I build my apps as plain Java EE 8 apps with a small Quarkus runner module. Your team presumably already know Java EE so there should be no re-training required.

regarding performance comparison I would suggest you take a look at this independent study https://horizons.carrefour.com/next-gen-infra/efficient-java-in-the-cloud-with-quarkus There are already Red Hat customers that are going into production with Quarkus based microservices