You can play around this stats
here. Yeh he's generally more effective on serve.
You can also check tournament performance at tennis abstract, and in terms of effectiveness there's just not much meaningful difference between Djokovic now in Slams and Djokovic during his "first prime" starting back in 2011. It's easy to check performance there by tournament, rather than just bundling the whole clay season or whole hard season. Of course Djokovic can no longer pound out a season for like 90 matches and maintain an amazing level, so I'm just mainly interested in his Slam performance level.