There's a saying - depth buys you regular season wins, cores/stars win you championships. KD is a better core player to have. At the same time, I completely agree that Cam/Mikal likely help us to a better than 13-10 record right now, and those draft picks could have been paired with CP3, or some other contract to get a more depth.
It all comes down to this - THe Suns have had many many great regular season teams. They've never had a scorer like Durant, not at least at that position, with all due respect to all the great players in the past. Durant is a proven winner as a #1A option, to another co-star. Book and Durant, just by being 1 and 1A, are enough to win you a title IF the pieces around them are good enough.
Here's our issue, the rest of our roster, the Beal trade etc. it may not be good enough. That's why we may regret letting those guys go. However just in terms of looking at it from a title perspective, I think we got closer to a ring with this trade. Especially in a playoff setting with match ups and all those little things that come into play. The real issue is our team lacks depth and is way too top heavy. The way this roster was put together, unless the 3 stars stay healthy, we won't have a strong regular season. We just don't have enough talented players after them. Other teams have better depth than us, more weapons and their stars seem to stay healthier.