Strongly disagree with "full teams can and have built huge java projects just by using the intellij project wizard and maybe a tiny bit of Gradle from stack overflow." I wouldn't want to work with someone who doesn't understand how build systems work. Specifics are irrelevant but knowing how to work with one build system means you don't have some vague textbook picture of how it works but you actually had to see it how it glues together. IDEs are nowhere near good enough to abstract that complexity away and it's a big part of day to day work.