For small projects, DI is easy done by passing things via the constructor. If multiple things need to get wired together, pull that wiring logic out into its own class or method (FooBuilder.buildDefault()). If things start to get tedious, that's a really good time to stop and reflect on the design choices. That stop-and-reflect opportunity if often lost when things can be simply AutoWired together.

Spring does this my examining the class path, casting it to a urlclasspath, finding all the zip/jar files, unzipping them and then parsing the byte code.

Interestingly the set let spec added annotation scanning too. And now if your not careful you jar files get extracted three times. The JVM, the server conteainer and spring all repeating the same work.

No wonder people think java is slow to start up.

In general I think, it is wise to keep the standard library small, because innovations are easier to implement in libraries. Rust is a good example for this style.

I agree with you, that Java should have had first-class function from day one. Ironically this was considered by the language designers, but they decided that it would be too exotic for the average Joe. OOP was a hype back then ...