Sad to say you have a really bad attitude and view about this. Hollywood and other things have really sensationalized and stigmatized demonization.
Yes, sometimes it really is that bad. But think about the woman in the temple doubled over. Her sickness was caused by a demon. Jesus set her free. She wasn't behaviorally like the guy in the tombs by any stretch.
The guy in the video points out that just because you have a demon or demons doesn't mean you're a "bad person" or some "raving maniac"; it's simply understanding how Satan works.
Most people right off the bat reject this for exactly that reason; they think that saying that someone has demons is some kind of value judgement on the person.
Jesus didn't do this, and I'm not doing this. You should really let go of that view because it's almost as though you're esteeming people who have been demonized as somehow lower than the people you mentioned with illnesses. This is wrong.
And no, I disagree that the sick people lack faith in all circumstances; the fault lies with the person praying for them. If someone prays over someone else, and they're not healed, it's unbelief on the part of the person praying, plain and simple. Jesus said this.
There is also no scripture that teaches that we're led into all truth through sickness. This is the Holy Spirit's job, not disease.
If those people you mentioned where with Jesus back in the day, he would have healed them because he even healed the daughter of the woman who wasn't even in covenant with God. Praise God that Jesus IS here today and is the same yesterday, today, and tomorrow.
But some people need REAL help, and learning about deliverance has been breakthrough for me. I've had several come out already. Someone else here had suffered with anxiety for a long time, and was also delivered from it. The person felt the spirit leave. The person was set free.
I also used to believe demons were rarely the cause, and that Christians couldn't have demons inside them, etc., but I've since learned that this is all traditions of men and actually not founded on scripture.
Again, some will receive it and some won't. Fair enough.