New Discovery, For Me At Least

Mat 17:19-21 NLT  Afterward the disciples asked Jesus privately, "Why couldn't we cast out that demon?"  (20)  "You don't have enough faith," Jesus told them. "I tell you the truth, if you had faith even as small as a mustard seed, you could say to this mountain, 'Move from here to there,' and it would move. Nothing would be impossible. "  (21)  [But this kind of demon won't leave except by prayer and fasting.]

I think, no I know, that there are many Pentecostal Denominations that using "fasting" as a means to gain God's power, and I'm not going to get into the doctrinal rights or wrongs of it, but I think we have missed the boat.

The ass-u-me tion is that the prayer and fasting was suppose to be exclusive done by the people trying to "cast out the demon."  But is this correct?  Something I just learned about is here, and here,

This was something throughout the ages, yet it seems to be played down today, why?  Or could it be this  just wasn’t known by me?