Hmm. To be honest, I think the title fits perfectly. It would be pretty impossible to make a 'perfect' CTF level. Or any other level, for that matter. However, it would be interesting to try.
I've thought about what makes levels have higher ratings, and I agree with the points you mentioned above. A great CTF level would be versatile enough for varying numbers of players, reward strategic players, and that sort of thing. But I really think you're going to struggle to make an ideal level. After all, it's a matter of the reviewers in the end. Not saying that people couldn't make a level that's actually worthy of a 10 and most people will agree on, but it would be incredibly difficult.