In my view, Baz = Class.new doesn't really "Start a class or module definition." it creates a class but there is no definition of it, no body.
Though Baz = Class.new { ... } would arguably start a definition/body, but then so would Baz.class_exec { ... } and that seems less reasonable to catch with a :class TracePoint.

I think unless there is a good motivating example to change behavior (which could be incompatible), it's better to just document it better, so I'd suggest opening a PR to document it better.