I also have 20+ years of experience and haven't seen that type of code either.

I am however struggling to understand an over engineered Rust "micro" service at work. There's no language or framework that is free from this.

Maybe it's because I have not worked in typical enterprise companies?

Spring Boot can be a really quick way to get things done. My current job is not in enterprise, but we use Spring Boot for most of our services, and rarely have issues related to Spring itself. We have micro services handling many transactions per minute and starts up within 10 seconds. The CPU usage is low and decent memory usage, even on the small pod sizes that we use. There are ways to reduce the startup, but we do not have the need. The code is easy to reason about and new hires are productive within a short time.