There's always a nuance to this. A singer may, indeed, be a technically awful singer, but they perform material that is popular.
There are performers whom I wouldn't want to see, but a bloke with a 40 year career is clearly doing something right. Even a poor technique needn't be a barrier to greatness or popularity. The folk who play instruments around their knees are displaying poor technique, but seem perfectly capable of becoming legends.
It's all very subjective. After all, if it was down to sheer ability, I'd be a musical god, but somehow I'm not! 🙂