@Doctor/Lawyer Red Devil - most welcome, I think you'll like the below as well.
His serve ain't as good, but the 1st serve and 2nd serve combo is plenty good combined with a vastly better ROS than either of them. If you're hoping for Novak to go downhill fast, I think you'll be truly disappointed.
Look at Federer's career post turning 29 (Novak's age now).
US 2010, lost to ND
AO 2011, L to ND
FO 2011, L to RN
W 2011, L to JWT
US 2011, L to ND
AO 2012, L to RN
FO 2012, L to ND
W 2012, W
US 2012, L to TB
AO 2013, L to AM
Rest of 2013, irrelevant
AO 2014, L to RN
FO 2014, L to EG
W 2014, L to ND
US 2014, L to MC
AO 2015, L to AS
FO 2015, L to SW
W 2015, L to ND
US 2015, L to ND
AO 2016, L to ND
FO 16, NA
W 16, L to MR
That's 11 losses to two of the greatest players to play the game, Djoko and Rafa (8 to Djoko), who were in their peaks and primes at the time of the losses. Plus one to Murray and one to Stan.
Now tell me, how many of those 11 slams he would have won, had there not been younger potential GOAT-candidates standing in his way? I dare say, more than a handful (and that's being conservative)
Now tell me, who's the potential GOAT-candidate or merely true ATG, who's supposed to "steal" the slams from Djokovic?
Andy's as old and seems to have developed a huge match-up disadvantage in recent years (though there's a slight chance, Lendl can fix some of that), Stan is older and somewhat inconsistent, Rafa is potentially done, same with Fed and he's shown he can't beat Novak in best of 5 anymore.
So again, who's there to stop him consistently? Raonic? Nishikori? Kyrgios? In order for a player as great as Novak to stop winning, someone needs to step up. As someone did vs. Fed back in the day. I just don't see who this someone is or these someones are.
Now that's not saying, that we've seen the last Querrey defeat from Novak. Fed also lost to Berdych, Tsonga, Stakhovsky and Robredo. But when he did go deep, Novak was always ready to stop him. Who's the player, who's there to stop Novak, when he does go deep the next 2-4 years?
Hence -> quite a few slams for Novak in the next 2-3 or more years.