The eco system is a huge force multiplier, and is constantly evolving. Spring Boot simplifies that a lot by simplifying the setup to the point where you often only have to add a single dependency, and everything is configured with default configurations (which you can change if necessary of course)
Just look at all the different projects under the Spring banner: https://spring.io/projects
One example is the new Spring AI, where they have abstracted a lot of functionality and you can change providers (OpenAI, Mistral, AWS, Azure, Google) easily.
It would be hard to convince some people of this, because "everyone knows Spring is enterprise". Unfortunately many only have experience with legacy companies, bad code or through reading old blog articles, and base their opinions on that.
It's actually something you need to have experienced yourself to recognize the possibilities.
It may sound strange, but I enjoy going through the long list of projects in the Spring web site. I almost always find something cool and is surprised at how much they can simplify complex functionality
The learning threshold is also relatively low, because they tend to use common best practices in the framework.
I like Kotlin, but the lack of checked exceptions really kills it for me. Exception safety is a bigger thing for me than null safety.