I've used Flask for single file sites with 10-250 lines. It's great (ish). What's bad about it? Your saying it's only good for writing large applications? How so?
Your contention is that it's only good for small sites. I'm saying it's good for any sized site as long as you actually know how to RTFD and program in Python.
Django is no different. Django falls apart spectacularly in the hands of people who can't program.
Flask is, of course, more powerful than bottle, and has less batteries included than Django. Saying Flask is good for 100 LOC sites is terrible advice, no matter which way you try to slice it. It isn't. It's widely-used and well-maintained.
Don't get me wrong, I like Django as well.