Goodreads rating system is useless anyway. It's 'out of five' which means most people will give a good book a 4 or a 5 star - it's not like IMDb's more nuanced 'out of ten' rating.
They also display a bespoke meaning for the stars (i.e. 3 doesn't mean average), so for those that follow that meaning, their ratings will be different.
I find it's still a fairly good indicator. Last time I was looking for a new author I went back and compared the author's average rating. Authors I like were 4+. Authors I think are OK scored about 3.5. Authors who I won't read again were generally 3 or so.
Perhaps 'useless' is a strong word. It's good for getting a general idea but too many books hover around the 4 mark. Whereas with IMDb anything 6 and above is worth the risk.
They also display a bespoke meaning for the stars (i.e. 3 doesn't mean average), so for those that follow that meaning, their ratings will be different.