Why is the notion that some cognitive ability needs to be developed to acheive full potential controversial for you?
The phenomena we are discussing is, to date, mostly defined and categorized based on subjective (self) reports. Given that, until we actually do experiments where we analyze brain patterns over a period of time and clinically prove that it is not true that a developmental methodology can alter brain patterns of subjects when attempting internal image formation, we can not summarily dismiss subjective reports that claim a degree of improvement.
I believe in a plurality of human experiences, they do not, because they experienced one thing different. It's a specious argument, just like all the people rejecting the idea that other people can have a different subjective experience (based solely on their own personal experience) in this thread.