True that's a fact but Hayley is an average singer may technically be an opinion but it's also fact.You can have an opinion on talent but many times those opinions are wrong for instance more people would say BillieJoe Armstrong is more talented than Steve Vai however they're wrong,what they should say is I prefer BJA over Steve Vai but Steve Vai is a better guitarist.
Okay, so you think Hayley is simply an average vocalist. You have every reason to believe that.
I think Hayley's better than average and there's reason for me to believe that.
I also agree with you about those other artists you listed before, especially Sharon den Adel because I love Within Temptation. lol.
And that's all that needs to be said.