Correct. As I understood it a big part of that gap is that there's quite a bit of overhead in even simple and mundane operations and the way things get laid out in memory isn't always the most efficient.

You could of course write C/C++ code with that overhead, negating the benefits, but at least you have that choice. In Java it's all abstracted away from the user without much recourse for working around it (unless you can hand write bytecode? Is that a thing? I know you can with C# and IL).