Build scans can give you insight into the order that tasks run, including any that run in parallel. They do not provide access to the input and output values though, sorry. That definitely sounds like something that would be useful!
I also think a visualisation of the task dependency graph would be handy. This old forum post has a couple of links to community plugins that may help. Hopefully they have been kept up to date and work with whatever version of Gradle you are using.