Take a close look at your serger thread. Most are very uneven with thick and thin spots. In a serger seam, the multiple threads give stability, so the strength and evenness of the thread isn’t an issue. That isn’t the case in piecing or quilting. Just go buy a cone of a high quality piecing thread like Superior Threads So Fine 50 wt. You only need a cone of beige to do pretty much all piecing unless you do a lot of bright white quilts. It is amazingly inexpensive per yard if bought on a cone.