My first exposure to FMQ was a class that I took on stippling. Hard as I tried I just couldn't get it and kept boxing myself into a corner and it was a big no no to cross over stitching lines. I also had an older machine with a generic hopping foot. I swore off FMQ that it just wasn't for me for years. I became quite proficient at doing curves and fancy designs using my walking foot.
A few years ago I bought a new machine with a wide harp. I started looking into FMQ more and started doing curves, loops, hearts and such and found that with the better machine and staying away from stippling I could do a decent job. I still can't go without some lines to guide me but it works.
Bottom line I think some shapes are easier for some than others. Practice does improve results. Don't give up until you've tried different shapes to find your rhythm.