To make the playoffs, it would have taken EVERYTHING going right. JJ and Bender would have needed to be actual NBA players, Booker would have needed to be healthy and a clear all-star player, Ayton would have needed to exceed every expectation (which, in all fairness, he has done), Ariza would have needed to have his best season in years, etc.
I don't think it would have taken all that. Booker as a clear All-Star, Ayton producing like he has, Warren improving like he has, and the entire team playing some of the best defense the Suns ever had would be all it would take. If we were a top 10 defensive team I think we could make a playoff push. That would require Booker and Ayton to be better than they are defensively but if Ariza was a lockdown defender like he's been at a few stops throughout his career, Jackson became the defender he was touted as before the draft, and a strong rotation of defensive PG's, we might have been a top 10 defensive team. With Booker, Ayton, and Warren we have the scoring to stay close to just about anyone but we can't get stops on the other end, at all, so it doesn't matter if we score. This year around the league it's largely been a first team to 110 wins, instead of 100, and the Suns could hit that but not while keeping their opponents scoring less than them.