He's having a terrible year by his own prior standards. His W/S/48 is only .045 (lower than even his rookie year) and a lot of his advanced metrics (VORP/BPM/OBPM/DBPM) are all below zero right now. 44% from 3 last year to right now 34% from 3. Not a complete liability out there from outside, but definitely a prolonged slump as the sample size is no longer tiny. Klay benefits greatly from Curry's gravity so having him out some time definitely hurt. I don't know if this metric is publicly available, but there is one that clearly shows the quality of shots Klay gets (basically how open he is) with Curry on/off the court and it is a significant deviation beyond the average 2 guard on other teams with any particular player (star or not) on/off the court. He also benefits greatly from Green's play making ability and Green is badly struggling too this year. Green is costing himself a lot of money in two years with this year's play so far. Durant I think is having a pretty good year but even he's gone slightly down from 42 to 37% on 3s this year so far. His ORtg and DRtg were incredible his first year in Golden State, but last year and this year so far they are worse than any of his prior five years before these two. I am sure Golden State will pay Klay, but I'm not sure it's a 100% slam dunk good value.
But having said that, Golden State isn't exactly in panic mode. Despite their struggles, their overall offensive efficiency is right now #1 in the NBA. (They were # 2 last year behind Houston) Just like last year, they are still #1 in team true shooting percentage. But their defense was always top notch before Durant came and then great his first year there, and even last year their defensive efficiency was 9th in the league. Now so far it's 19th. Their opponent true shooting percentage last year was # 2. Now it's 12th. They are maybe a decent but more fair to say average team on defense right now, and I think some of that is frankly complacency and four prior years of playoff grind. (This is also partly why I appreciate LeBron playing so well every playoffs considering the extra grind year after year, it's tough) But some of it might be real drop-off from Green and Klay to a smaller extent and their bench is now weaker too. Let's see them after the All-Star break and if they turn it up another gear especially with Cousins coming who looked at first like just an overkill luxury (like an extra cherry on a perfect sundae) to maybe now a real need to win the title.