Spring Boot absolutely yields write-once throw away, and you _must_ consider the source: Pivotal is a contracting shop, so it's in their interests to hook people into an ecosystem that they happen to be experts in. I'm surprised this fact is lost on most.
I don't know Spring and Spring Boot well enough to pass judgement, but this situation generally arises in software when you have a language or framework that's reasonably expressive, where the language has a lot of sigils or keywords and it has "shortcuts" that you have to grok before you can really understand codebases that use those shortcuts (like annotations or heavy/excessive use of design patterns). It leads to software solutions that are only well understood by the original authors due to their specific knowledge and problem solving approach and anyone who comes along later must have the exact same overlap of knowledge and skills otherwise they'll find it easier to start fresh. This includes the original authors if the time lapse has been long enough.
This often then leads to the next phase of miserable software jobs, the second-system effect.
* https://www.axios.com/trumps-timeline-always-two-weeks-15133...
* https://www.bloomberg.com/news/articles/2017-06-06/in-trump-...