I think Kyrie is the best iso scoring guard in the League. I don't know if the stats bear that out but I can't think of any other G who has the combination of shot creation and difficult shot making.
Yup, and that's an invaluable skill to have in high leverage spots when things get more compact & less is called. You clearly notice a difference with a guy like Curry - the oxygen that's there for him in the regular season tends to dissipate against teams who are well-coordinated against Golden State's motion and screening algorithms.
It isn't that Kyrie is the best player in basketball so much as his combination of handle, agility, and shot-making that you mentioned make him context proof. There is no situation, no defense, no anything that can negate what he does well. With a guy like Durant, you always expect his weaknesses - handle, body, etc. - to be illuminated when it's winning time. Plus, the fact that he's a guard empowers him with an autonomy that doesn't exist with a big or even a wing - if you're throwing the ball into Cousins late in the game, you're going to have to be pragmatic about it, and by the time he gets it, now maybe you have a double coming and it's too late in the clock to do anything about it.
I don't have any stats to back this up, either, but shooting percentages go down in high leverage spots because anything and everything that can be exposed - both individually and within the team structure - does. That doesn't seem to exist with Kyrie and it makes him unique.