But it's not that simple. I was very high on Doncic, but I would have picked Ayton too. There was no question that Doncic would be a good player, but he had questions surrounding him too. There was no guarantee that he could get into the lane in the NBA, there was no guarantee that he'd be able to get that step-back three against the NBA competition, there was no guarantee that he would have been able to play the primary ball handler role against the NBA competition, and the list goes on. Nobody questioned his work ethic, his "motor", or anything like that, but there were legitimate questions around his lack of speed, quickness, etc.
Ayton is a prototypical modern center. He has the size, his body is incredibly well-developed for someone his age and height. He has inside game and he can hit a mid-range jumper. He can guard the perimeter as well. There were no questions regarding his size, athleticism, ability to score, rebound, etc. Concerns around him had to do with his "motor" and work ethic.
It would have been perfectly reasonable to pick Luka, and it was perfectly reasonable to pick Ayton. Nobody thought that Luka would be as good as he is. I am 99% sure that 90% of the teams would have picked Ayton with the first pick. It's easy to say they should have drafted Luka now, but at the time, either pick was perfectly reasonable. You are gambling either way- you are counting on Luka to be able to do in the NBA what he did in Europe, or you are gambling that Ayton is going to develop into an unstoppable big man. Another thing to consider is that while Luka has been amazing, Ayton has been pretty damn good too. It's not like they passed on Luka to pick Chriss, Bender, or Josh Jackson. Ayton had a historically great season for a rookie Center of his age. Luka is obviously better, but it's not like Ayton sucks.
It's not always clear as to who the best player available is. Suns made the wrong choice, but it was a perfectly reasonable choice.