Since 2013 Nadal only leads Djokovic 6-5 on Clay so Djokovic has certainly made inroads but obviously Nadal wasn’t at his best most times as Nadal plays his best on Clay he wins it’s that simple. Nadal wasn’t really out of form in 2014 though if we are being honest yes 2015 he was a mess but of course it helped that Djokovic didn’t meet Nadal in 2017 on HC.Too much has been made of Nadal failing to beat Djokovic at hard court since 2013 in this and other threads. It is just a victim of circumstances. Leaving out Djokovic's win in the French 2021, the only reason why Djokovic has beated Nadal on clay more recently than Nadal beating Djokovic on hard courts is becasue Djokovic has met Nadal when he was totally out of form (2014-2016) whereas Nadal did not meet Djokovic when he was out for form (2017-to mid 2018). Djokovic is overall better than Nadal becasue he is better than him at more surfaces but neither of them has made much inroads in each other strongest surface since 2013