Two things - almost NO way Doncic is there at 5. Memphis probably takes him over JJJ, first and foremost. And even if Memphis wasn't enamored with Doncic, at that point teams KNOW the Mavs will take him, so someone would have given Memphis a great offer to move ahead of Dallas for Doncic. Atlanta was fixated on Young, but Memphis would have been fine with trading down and pass on JJJ if given a good offer. So if Dallas wanted Doncic they had to trade up.
Second, Doncic is a different tier of prospect than everyone but Ayton. If you think he's your superstar, you go and get him. Even if the Mavs liked JJJ/Bamba/etc, they had Doncic in a tier above. I'm all in on Doncic too. You always make the move for a talent the caliber of Doncic, and I'm glad to see the Mavs didn't waste this chance to add a premium talent. And the fact the Mavs got some protections on the pick in case of catastrophe is just icing on the cake.
And for the record, the Mavs trade for Doncic is unanimously praised by basically everyone around the league and the media. It was a great move.