Up until I acquired a Janome Sewist sewing machine with a one step button hole facility I had always been able to produce near perfect buttonholes.
I remember that with my first Singer sewing machine that when I did buttonholes I had to swivel the fabric around when I had completed one side of the buttonhole before I could proceed with the other side because there was only forward sewing and no reverse button. This actually produced pretty fab buttonholes. Both sides were balanced as they were sewn with the same forward facing stitch. Because it used the zigzag setting on the machine I was also able to vary the width of the buttonhole creating narrow ones for delicate fabrics and chunkier ones for woollens and the like.
My next Singer sewing machine had a four step buttonhole facility which I thought was great progress and although it was I did find that I had to adjust settings in order to get a balanced buttonhole and they were all the same size regardless of what fabric you were using.
With the Janome I thought a one step buttonhole would be a boon and speed up my sewing time. How wrong I was. It works okay so long as there are only two layers of fabric with a piece of interfacing in between. However if you try to sew a buttonhole next to a seam (on a collar band for instance) and no hope. All I end up with is a thick wad of thread. I have never before had to unpick so many buttonholes and redo them. So rather than saving time it has actually made the sewing process longer.
I had a cheap second sewing machine (now donated to a relative) that did much better buttonholes using a little shoe foot with markings for buttonhole sizes. I therefore decided to purchase one of these and try it with the Janome. I can sew one bar tack and the left hand side of the buttonhole but then have to manually click the return device for the machine to stitch another bar tack and the right hand side thus creating a two step buttonhole.
It does seem to have solved the problem and I have now practically given up with the one step method.