Clarke is almost right with the 'two boomers, two good imports' theory (also known as the 'six tall blacks, two good imports' theory).
Looking back over the years, I think it is more of an 'at least three stars, complimentary role players' rule. I think it works for most teams in recent history:
2010 Perth: Redhage, Lisch, D Martin, Cattalini
2009 South: Worthington, Ingles, Donta Smith
2006 & 8 Melbourne: Anstey, D Mac, Thomas
2007 Brisbane: the most stacked team of all time? - Sammy Mac, Ebi Ere, CJ Bruton, Gibson, Rychart
2003-5 Sydney: variously Nielsen, CJ Bruton, Heal, Chris Williams, Jason Smith, Ebi Ere, Kavossey Franklin, Rolan Roberts and several hundred Boomers squad members (Barlow, Kendall etc)
2002 Adelaide: Maher, Farley, ?? - Exception to the rule?
2001 Wollongong: Saville, Charles Thomas, Melvin Thomas
2000 Perth: Rogers, Vlahov, Grace, Fisher, Timmons
98-89/99 Adelaide: Mee, Maher, Brooks
Anyway, the Sixers can really only boast one boomers-level or 'star' player in Ballinger, and otherwise have a team of role players. That just does not cut it. Ballinger's weaknesses are exploited as he does not have other stars to draw the pressure off him or pick up the slack on an off night.
Remember even Khazzouh, the runaway MVP favourite, is on a team with a losing record because he lacks any support at the other positions.