No, the proto-Masoretic excludes the deuterocanonical books.
I’m a little confused about how you’re trying to make sense of what I initially wrote and the excerpt I included from Schiffman’s book. When the scholarship notes that a particular manuscript is ‘more proto-Masoretic’ or ‘more Septuagintal’, it has nothing to do with the canonicity of the books involved. It’s about whether variant readings in a document (rarely a complete book, most often a loose sheaf or a fragment) are more characteristic of the proto-Masoretic, Septuagintal, proto-Samaritan or whatever text-type. They are distinguished on the basis of individual words and sentences, not the inclusion or exclusion of an entire book.
In addition, the Septuagintal text type was not a single, harmonious tradition. There are many, many different recensions and translations. For example, the Church (including Orthodox) does not use the traditional Septuagintal book of Daniel, which is of the Old Greek text type. We instead use the later 2nd century AD translation by Theodotion, a Jewish scholar, whose translation is much closer to the Masoretic Text.