I dont think JO is anywhere close to Chandler. I don't even believe he can play a full 80 games. Adding a true starting 5 who we can count on is the biggest area of need, not CP3 or backup SF.
Last season, Chandler played 74 regular season games, but before that, he played 54 and 41 in the previous two seasons. (He did play in 70+ games in six of his first seven seasons.) To a certain degree, the Mavs were lucky that Chandler was healthy, given that he seems to have recurring ankle and back problems over multiple seasons.
Jermaine O'Neal is more likely than not to miss a good chunk of games, but there is a decent chance he is healthy for the playoffs.