They have met 16 times in total in slams
8 times at RG and 8 times at the other three slams combined.
So if Nole fans claim Djokovic to be superior to Rafa off clay, the H2H distribution is balanced. 8 matches with surface advantage Nadal, 8 matches with surface advantage Djokovic. Both players have had the exact same amount of matches on favourable surfaces. Nadal leads 10-6. If Nole is clearly superior to Nadal, he should dominate his 8 matches and win a few on Rafas surface, right?