My suggestion is to allow quantity link fields to be directed to one of the source files only, not all, as another option in the drop down like below…
OR, (even better) to be able to dynamically change these source files by putting the relevant filepath in a field, i.e. column A has the filepaths, and the workbook can "point" at the file within the filepath… this way, a matrix can be utilised for creating the takeoffs. Below Example:
This would enable a much larger uptake from the company I work for and improve workflows immensely.