A friend of mine told me that in yesterdays sermon, his SSPX priest said that the Low Mass is a recent innovation from the 14th century and that the Sung Mass is much older and original form of the mass. He said the priest actually went so far as to belittle the Low Mass.

That information from the priest is totally incorrect.

The Low Mass originated in the late 700's, that is the 8th century. Anyone that questions this, can do some research on all the new churches built in the 800's (9th century) which were built for the first time with many side altars to accommodate the numerous masses which would have been offered every day by the priests due to the change.

The Sung Mass, Misa Cantata is from the late 1700's, so it is actually the Sung Mass that is a recent change. It is this mass that is celebrated at the church my friend attends, along with a Low Mass. His priest is conveying erroneous information to his congregation, either from ignorance or worse. It was not till 1960's that permission was granted for incense to be used at a Sung Mass (Missa Cantata), another innovation.

It is the Solemn High Mass that is the original mass, and it requires three ministers. This is why they are rare in traditionalist chapels.

Misinformation is bad, and there's nothing wrong with a low Mass, but he was probably not intending to make a statement specifically about the particular form of the Missa cantata. I think most traditional priests, including the SSPX priests, know at least the general rubric history of what we now call the Missa cantata.