Is success due to hard work sustainable in academic research?
I can't say whether 10-12 hours per day is right for you, but caution you to consider your health. If it suffers, then everything will suffer. 

But "intelligence" alone is overrated. The path to Intelligence, actually, runs through Hard Work. 

I once got the results of an IQ test (I hope they don't do this any more). The printed results said that I was a bit above average, but not outstanding. They recommended that I set my goals at community college rather than university as I'd be more likely to succeed with more limited goals. 

About fifteen years later I earned my PhD in mathematics. So much for prediction. 

More about me. When I was young I was pretty smart but was disengaged from school. My life was elsewhere. I saw no point whatever in school. It was in the second or third year of secondary school that I had what I considered my first positive educational experience. But then, I started to work. And I worked hard. 

But, you need to use the hard work to seek insight into what you are studying. The work, itself, isn't enough. But the insight is very unlikely to come to most people without the hard work. 

Again, though, don't neglect the wider picture. Get enough sleep. Get enough exercise. Seek feedback on what you do from those who know more. Find a mentor (or three). Ask a lot of questions. Take a lot of notes. 

And don't try to work past the point of frustration. The work will be very inefficient. Take a break for a bit. Then come back to it.