Canned feedback in online courses. What educational theory does that?

I just ran across an example of a means of feedback that I found a bit disturbing, but perhaps necessary in some cases.

In the past when I have needed to give feedback on assignments in classes I am am teaching, I have individually crafted responses. I will admit to having reused phrases when running into the same issues in essays over and over. I tend to treat these opportunities as "teachable moments", and so there is a requirement on my part to address the issues in a personal manner reacting to the individual and what I know of them instead of just the question or issue.

My experience is based upon class sizes that were never in excess of 50 individuals. That is my caveat.

But what do you do when you are dealing with the work of say, 150 individuals and you only have so many hours in the day?

Apparently a popular answer to this is to create a document with canned responses to assignments or problems. It is simple enough to copy and paste from the document into the feedback section of the assignment or the discussion and then customize with student name and any other information that is pertinent. In addition some instructors use macros to insert specific feedback into documents. These are interesting ideas, though I am hoping to never be in a situation where I need them. In an online course that is built on a basic constructivist model the primary role of the instructor is that of guide and/or curator and/or facilitator and/or concierge, which demands individually tailored interaction with the students.

Given that the ideal class size (the last time I looked) in an online class was something in the late 20s to low 30s, I wonder if these larger class sizes can meet the definition of constructivist, or are they constructionist, or something else?