This is very true, I've been teaching for 23 years, never had QTS, never will, I have a BSc MSc & PhD in my subject (Engineering), have taught at HE & FE level and been head of Science in an independent school for 12 years, only one of the 10 teaching staff in my department have QTS, all are exceptional at what they do.
Having a deep subject knowledge is the foundation, having the gift to convey that knowledge to others in an engaging and successful manner is key, I don't think you can learn that - you either have the enthusiasm and gift of communication or you don't.
Teaching has a lot in common with stand-up comedy, which I guess is why so many stand-up's have been teachers. You get up in front of your audience, the class. You have a broad plan of your line up, but you have to bend with the wind and improvise as needed, maybe a piece of information you thought would sink in easily just isn't, so you need to adjust the pace, change the delivery, or go at it from a different angle. You can't learn that in any effective way, you either can or can't.