Isn't this how the game was designed, to
not be easy and to mimic real life?
I've had this problem, too. At first I had limited consistency using my thumb on the R stick to swing. Then yesterday I was
all over the place -- I was only hitting the fairway on every other hole.
But yesterday I tried a new "technique". I think I have more control of my R stick swing by holding my right hand parallel to my controller, and gripping the R stick using my thumb & index finger. (Thumb on bottom, index on top.) So far I seem to have better control -- and consistency -- of making near-vertical swing "lines". Of course, I do have some deviation off the line on every swing, but I seem to have more control than I did when just using my thumb...