Someone who has practiced karate for 6 months can defeat someone who has practiced TJQ for 6 months????
Maybe. But only maybe.
I've know people who have practiced karate for 6 years who couldn't fight their way out of a paper bag if you made it wet, gave them illustrated instructions, good lighting, infinite time, let them use both hands and then gave them a sharp knife for extra measure.
By the same token I've know TJQ students who could apply some pretty advanced techniques after six months of diligent practice with a good instructor.
It has as much to do with natural ability as time served. Some people just "get it" very quickly, others do not.
I didn't, I have barely started to, but that doesn't mean everyone won't.
Sweeping generalities about anything are probably not a great idea. I would imagine that most people who study any style of martial art take more than six months to apply them in good order.
If defeating an enemy is your goal, buy a gun it's much faster to learn. If learning to be in control of your body and your mind is important to you, then practice TJQ, though it takes longer the results will be better in the end.
However, telling people that they will not learn to defend themselves well with TJQ may not be a good idea. First, it's not true. Second, it may discourage some who are seeking a good path.
You will learn to defend yourself, it will take longer than other ways but once you get there you will be better prepared.
Learning TJQ is a long, slow process that requires dedication. If you are dedicated then there will be no opponent you cannot defeat.
The funny thing is, victory and defeat get redefined along the way. You will see them differently when you're done then when you started.