Given what KL did in the 2014 NBA Finals (Finals MVP, outplayed Lebron as I recall), and how well Spurs looked in game 1 of last year's conf finals vs. GSW before getting injured, to me, a healthy KL is in the same class as Lebron and Durant, and a notch above Giannis (who hasn't done anything of note other than fill up a stat sheet; let's get real).
The issue is his health. If he is healthy, he is a top 3 NBA player. Poll NBA GM's and pretty sure vast majority would agree with that ranking. Now Giannis may project to have greater future value. I get that. But in a play-off series today, I'd take Leonard.