Those things are not separate. Though I agree that Doncic isn't the athlete that Simmons is, but I don't think he is far off minus leaping ability. Either way neither one would be guarding PGs and if Doncic gets any bigger he could possibly play at the 4 in the NBA. He is already similar in size to many small ball 4s right now at 6'8" and 230 lbs.
Therein lies more of the problem. If he plays at the 4, at 6'8 and not very athletic, he'll playing against other small 4s, defensively he'll be at a disadvantage because most of the stretch 4s are athletic enough to play the position. And on O, he'll be going up against the same athletes who will make it difficult for him to create if he doesn't have the speed to get around them.
And have you watched Simmons? Simmons is FAST and BIG and EXPLOSIVE. Doncic is literally none of those. He's not even close to the same athlete as Simmons. There's literally no comparison between the two.
What I see in those highlights of Doncic and looking at his athleticism? I see Mike Miller in college... who everyone thought was going to be a star. 6'8. Could shoot... had "excellent basketball IQ", natural passer... was the point forward for the Gators team that went to the NCAA Championship Game. He went
FIFTH in the lottery. Ended up being a solid player... but that's it. That's what Doncic's game reminds me of when I watch his highlights.
That being said I would hope to get Ayton because he fits perfectly with team needs and is almost certainly the best prospect in this draft. Though if we are drafting with Ayton off the board I take Doncic and figure out how to fit it all together.
I will vomit if we decide to take a tweener, who's not athletic, not a great shooter... but has "excellent basketball IQ". A core of Booker/Jackson/Mike Miller 2 is atrocious. And it's just what I expect McD's ******* to do.