The main point here isn't the whole "Does YPG = PKK?" question. The poster's point is that folks who call Efrin the "weakest" canton are underestimating Efrin and overestimating Kobane and Jazira canton.

Efrin has spent a lot of time holding Efrin and training. The canton as a whole could benefit from a supply line to the rest of Rojava (and hypothetically, Iraq). They could really benefit from more U.S. air support. etc...

But they've held a line a long time against northern Aleppo opposition. There has been some back and forth between JAT and the other rebels with villages and towns east of Maryamayn and west of Mare, JAT and SDF put an end to that after they took Tel Rifaat and Menagh airbase in February 2016. In retrospect, may they should have taken Mare since Mare declared war against them, but at the time they were still trying to negotiate a non-violent turnover. That didn't work, but they also didn't press the attack.

It seems that Efrin SDF's actions have been more constrained by politics and trying to not be seen as undermining the FSA in northern Aleppo.

Now, they have decided to al-Shahbaa/Sheba Reservoir area. Something they have been talking about for awhile; and including al-Shahbaa representatives in the Syrian Democratic Council, etc... it would also be a necessary step for Efrin SDF to participate in an al-Bab offensive.

The poster's point is that people shouldn't underestimate the Efrin SDF--even if they have mounted few offensives in this war and haven't taken the impressive gains made by the Jazira and Kobane canton SDF.

And perhaps this under-estimation of Efrin SDF is related to the current rebuff of Euphrates Shield offensive towards Tel Rifaat.