In the past, he won much more Masters than Slams.
2011: 3 Slams, 5 Masters
2012: 1 Slam, 3 Masters
2013: 1 Slam, 3 Masters
—> 2011-13: 5 Slams, 11 Masters
2014: 1 Slam, 4 Masters
2015: 3 Slams, 6 Masters
2016: 2 Slams, 4 Masters
—> 2014-16: 6 Slams, 14 Masters
2017: 0 Slams, 0 Masters
2018: 2 Slams, 2 Masters
2019: 2 Slams, 1 Master
—> 2017-19: 4 Slams, 3 Masters
So since 2017, Djokovic has won more Slams than Masters. But from 2011-2016, he won 11 Slams and 25 Masters.
2011: 3 Slams, 5 Masters
2012: 1 Slam, 3 Masters
2013: 1 Slam, 3 Masters
—> 2011-13: 5 Slams, 11 Masters
2014: 1 Slam, 4 Masters
2015: 3 Slams, 6 Masters
2016: 2 Slams, 4 Masters
—> 2014-16: 6 Slams, 14 Masters
2017: 0 Slams, 0 Masters
2018: 2 Slams, 2 Masters
2019: 2 Slams, 1 Master
—> 2017-19: 4 Slams, 3 Masters
So since 2017, Djokovic has won more Slams than Masters. But from 2011-2016, he won 11 Slams and 25 Masters.