A Pharisee text is sectarian, as it is only for Pharisees. That is an interesting question. I would say no. But that would depend on how 'sect' is defined. I am willing to accept Josephus' tripartate division, and hence Hillel and Shammai would be part of the same sect.
Bad habits are hard to let go of.
I look to compare it with the Talmud to see what is similar and what is different. I concur with Schiffman that at that stage they were close to the Sadducees. That later they would be called Essenes is another issue. Though I doubt it, the Essene hypothesis may be correct. That is not a safe position.