His somewhat lackluster 2017 late-summer to fall season brings my opinion down a bit. Event by event:
AO: Excellent clutchness, but he dropped a ton of sets along the way.
Dubai: Lol
IW: Peak level; no excuses.
Miami: Solid overall level even with a tough draw; struggled a bit against Birdman and KyrGOAT but both played really well so props to them.
Clay season: ...
Halle: That final vs. Zverev was some pretty GOATworthy stuff; overall high level
Wimbledon: Hard to rank because while he did drop zero sets along the way, he wasn't at his grass court best imo and could have lost one or two sets. The Dimitrov match was a beatdown though.
Roger's Cup: Injured but still made the final; go figure.
USO: Not very good. Two five setters in the first two rounds and went down rather unceremoniously against Delpo.
Shanghai: High level for the most part.
Basel: Same here too.
WTF: Nope.
AO 2018: Good level all around but he got a very safe draw; you saw what happened when Cilic redlined for just a little bit later in the final.
Rotterdam: Nice performance, especially in the final
IW 2018: Meh. He should have won, but he was still a few notches below his 2017 version
Based on this, I'm willing to rank this stretch as 85% peak level (I voted 90%).