One of the problems with defining "good shooting" is that "good" is relative, but the reference standard is vague; IOW, "good" compared to who? From those who shoot maybe once a year, to the local regulars at the range, to competitive shooters, there's quite a range of "good". Even among competitive shooters, there's quite a range, so it's safe to say you're a "good" shooter if you're a competent competitive shooter, say marksman/sharpshooter level.
And as Japle suggested, "good shooting" also involves more than 1 skill set done under very controlled & stress-free conditions. Competition makes you a better shooter by forcing you to broaden your skill set under match conditions (read:
stress) and to be good at those as well.
Before competing, I was one of those who could shoot 25 yard cloverleaves (still can, btw
), but that's about all I could do. Fortunately, in the process, I developed a strong foundation in the fundamentals, so when I did start competing, I improved quickly, despite the steep learning curve.