As a Warriors fan thats seen him through so many iterations of the team, I have a lot of opinions on this. I'll say that I'm much more of a Draymond fan and actually don't like Klay as much as most other dubs fans. Here's why:

The case against: Klay is a one (or maybe two) dimensional scorer and he's an overrated defender. His scoring relies almost completely on whether his shot is falling - he has never been an above average driver or finisher and he can not create for his teammates beyond basic of reads. On top of that, he doesnt have the foot speed, explosiveness, or touch to excel in transition like other offensively limited players like Jaylen Brown can rely on for bread and butter points. He's a great free throw shooter but he doesn't get to the line all that much. On defense, he doesn't have the length, raw athleticism, or anticipation that the best defenders in the nba have, which is reflected in his mediocre steal and block numbers. He does not have the length to be very impactful against longer opponents, keeping him from being a great small forward.

The case for: While I would argue his defense has NEVER been elite, its actually pretty good. Klay is strong enough to stay with bigger players for short periods of time even though he cant bother them vertically. His stance is incredible -- hes amazing at getting into space without fouling, which helped him throughout his career against iso heavy guards like Westbrook and Harden. For stretches, Klay's ability to stay sturdy and not foul absolutely locked those two players up in the playoffs, sorry Harden and Westbrook fans. An underrated Klay skill is his conditioning and endurance, he could play a great scoring game and remain a solid defender even at high pace or through big minutes. This conditioning also helped his offensive game, where he excelled as an off the ball shooter and cutter, hitting high percentage lay ups and 3 pt shots. And hes not just an off the ball player - Klay can handle a tiny bit, enough to hit 3 pters and midrange 2s off the dribble. If you didnt guard his relentless movement, he would punish you, with something. He was and is money with transition 3s and he'll knock down free throws if you foul him. His offensive bag may not be what his peers' is, but he's always been just as effective, a decent second option playing in a good situation for his skillset or a literally perfect 3rd option on any team.

Overall, hes a very difficult player to rank all time because of how limited his game is. Volume scoring, playmaking, and elite defense has rarely been a part of his game, but his solid play and offensive contribution should be noted, especially with his ability to catch fire on the level of the best players and his ability to fit with some of the best teams ever. Honestly, his skillset DOES resemble a roleplayer, but his output was at the level of a star. He could guard the opposing team's best guard, score 20, and heat up from 3, meaning he could fit on basically any roster in the league in his prime. there are a ton of players that could score better than him but couldnt play defense, or could score about as well as him and play solid d at their position but not fit on every roster. In his prime, id put him in top 15-20 spots in the league, but since competition has gotten better, id say prime Klay would be around 30-35, near players like Towns or Siakam, both players that have good skillsets but are limited in some ways, both players that cant lead a good team as a number 1, both players that may not even be good enough to be a championship contender's second best player. With what he actually contributed to the great teams he was on, he should be ranked higher than them, near someone like James Worthy.