I'm generally able to adapt to new languages and technologies relatively quickly. I'm able to build at least simple applications from scratch and have at least basic understanding of all the component parts and how they fit together. I'm generally able to measure the benefits and drawbacks of individual pieces of technology and where to make certain tradeoffs when architecting an application.
Now, I still have a lot to learn and I'm sure I can't do the above tasks anywhere near as well as an experienced Sr. Developer, but based on others anecdotal experience at least this doesn't seem to be common in many Jr. devs