Absolutely terrific advice.
As soon as I read "_specific_ feedback", my eyes lit up.
Another issue with specific feedback is that "...should be red instead of blue" type feedback can derail a designers whole thought process, a thought process which usually doesn't end at the delivery of a draft, which is merely an optional stop along the way in the mind of the designer.
A designer might have ideas for how to address certain kinds of objections to a draft. For example, if boss says, "It doesn't match our brand well enough.", the designer might have some specific ideas that he/she came up with, in case that was a perceived issue. If, instead, the boss says, "It doesn't match our brand well enough, so add more blue.", then the designer's route can no longer be used, and an entirely new route has to be determined.
I use the railway analogy, because I think it actually maps exactly: Imagine you, as a train passenger, told the conductor (the person you've hired to be your railway professional) exactly where to go, and there wasn't a predefined switch for getting there OR the switch for getting to that exact location has already been passed. The only way to achieve this new route is to backtrack or build a new switch track, both of which are more expensive than continuing on the existing route to a location that also solves the passenger's problems.