If Shaq is as awful as some want us to believe, the Suns won't win the championship. If he really is as useless as his critics think, then they can have the satisfactionof chanting "I old you so".
If he can't play, then the Suns can go samll with Barnes or young with Lopez. That won't win the championship, but it might help a ffew years from now.
But what happens if Shaq is in decent shape? Will anyone say, "my bad". Of course not.
What about Shaq's defense? Yes, he was slow, but the Suns scheme was to push everybody into the paint and this was simply bad strategy. If Shaq is healthy, I expect he will do a good job. Granted, he's not a great pick and roll guy, but look at the defensive stats for Shaq teams:
Lakers
1996-97 44.1%
1997-98 43.9%
1998-99 44.1%
1999-00 41.6%
2000-01 43.8%
2001-02 42.4%
2002-03 44.3%
2003-04 44.0%
Heat
2004-05 42.7%
2005-06 44.0%
2006-07 44.0%
Prior to joining the Suns, Shaq's teams defenses never permitted higher than 44.3%. Last year that would have tied for 4rth best in NBA. When Shaq was in condition like 1999-00, it made a huge difference; but even out of shape and injury prone, his teams were pretty good defensively.
Losing Shaq did not HELP the Laker's defense.
2004-05 45.3%
2005-06 45.0%
2006-07 46.1%
2007-08 44.5%