I ask because Java in other large open source projects (Elastic Search, Cassandra, Android) and it really depends on how its being used (by Keycloak as well)
I've also come across GraalVM which can significantly reduce Java memory consumption (if that is something you are referring to)
But since you asked, basically Keycloak was by far the single largest component of our stack, which didn't sit well with me because by any measure, our application was far more complex than Keycloak.
At the time we were transitioning away from JEE to JSE microservices, and Keycloak was a full-blown JEE application with all the heaviness that we were successfully leaving behind; it took over a minute to start, while our other Java services would launch in less than a second. Of course this didn't impact production at all - but most engineering time is spent in development and testing, where this was a real problem, especially if we were experimenting with and learning about new features.
All of this contributed to my perception of heaviness.
Seems like your other Java services were not an issue though?