I believe it. Though my experience is that junior devs can be much faster at producing lines of code, and most of it's junk. Senior devs will always be faster at producing bug free lines of code, and certainly at catching more of the edge cases. Moreover, the best devs I've worked with know when not to code at all to solve a problem, which is a totally foreign concept to junior devs who seem to prefer coding to thinking.

When I look at code written by junior devs I often think 'dear god, how is there so much code that does nothing, and how did it all get witten since I last had a chance to look'.

Makes me wonder if there are parallels in writing. My understanding is that the most prolific authors can only write 8 publishable pages a day. I'd bet that amateur writers can produce more pages than that, but no page could be published without at least as much time spent by an editor.