Not true. A simple A/B testing between having a form and not having one will tell you the "what" but not the "why". If I decide to cancel my account and end up on that form page, then change my mind and navigate away, you have no idea why. You cannot accurately claim that I did so because I was frustrated or because I thought it was a waste of time.
This isn't really something that is subject to argument; it's an empirical question. It's measurable; a known quantity to people who have implemented it in an A/B fashion.
I'd be very surprised if additional friction to a cancel process had zero impact. That would be sufficiently surprising to be worthy of an article or paper.