Citation needed, one talkiing about hard disks as of 2008 at the earliest, or an equivalent magnetic problem.

I am reluctant to comply with demands for citations on something that is not particularly controversial and, more importantly, does not contradict the references you yourself provided. Apart from reading your own references (Gutmann and wikipedia) you can look at the most substantial criticism of the idea that there are real world agencies who could recover your overwritten data, that by Daniel Feenberg.

Gutmann mentions that after a simple setup of the MFM device, that bits start flowing within minutes. This may be true, but the bits he refers to are not from from disk files, but pixels in the pictures of the disk surface. Charles Sobey has posted an informative paper "Recovering Unrecoverable Data" with some quantitative information on this point. He suggests that it would take more than a year to scan a single platter with recent MFM technology, and tens of terabytes of image data would have to be processed.

His general point is that while there has been some limited success with playing with powerful microscopes the current process is so ridiculously impractical and unreliable that there is no chance any existing intelligence agency would be able to pull it off.

A supporting claim needing to be stretched as far as "well, it's not technically false!" still strikes me as not being a good example to try to persuade people with.

Not a position I have argued against, nor would I be inclined to.