Sean Palmer's Soul Stitcher is a fantastically flavorful and interesting class. While some abilities appear really powerful (the Tailor subclass's Quick Stitch), others appear really weak by comparison (Thread Cutter, the level 20 feature, is essentially a weaker Cutting Words). That being said, the overall balance of the class seems to be alright. Each of the subclass options (Dollmaker, Tailor, & Smokeweaver) offer very different utility to a party and I think it would be very fun to play this in a oneshot or to construct a very unique NPC.
Overall, the Soul-Stitcher offers a very unique character or NPC option for both players & DMs. The document is clear and the subclasses each offer a very distinct suite of features.