Control forces are very high requiring both pilot inputs
According to Boeing in Seattle, there is no non-normal manoevre in the FCTM that requires the use of two pilots on the controls. If there was, three pilots would have to constitute the normal crew in case one became incapacitated. The manual reversion approach and landing is relatively straight forward to fly assuming a competent pilot is flying. Some operators prefer that one pilot flies the manual approach and the other pilot handles the power. It was this policy that aroused the ire of simulator instructors at Seattle.
Some pilots have done only one manual reversion approach and landing as part of a typre rating then never practiced one again. It is these pilots that may experience significant handling problems and then complain of the danger. One pilot can easily fly the approach and handle his own power IF he is competent. Automation complacency has a lot to answer for - especially where almost total reliance on automation has led to a class of pilots that have lost confidence in their ability to handle something like a manual reversion landing.