GCSEs are no indicator of someone's intelligence to be honest
I know some people who achieved Bs & Cs at GCSE level but surprisingly achieving/achieved As & A*s at A'level.
I guess everyone just took GCSEs as a joke back then (including me) but that same approach couldn't be taken into A'level as its a whole new phase.
Also, i personally don't think achieving 10 or more A* means that you are a true genius. Being a genius comes in different aspects of live. Im sure not all the famous geniuses got all As during their education life.