and 2-3 zone vs. an outside offense... game over 99% of the time.
Well if you have a shooting team, than yes. If you have a balanced team and they have really good outside defenders, then it's not 99%. Know that with 2-3 defense, you will get no offensive rebounds, so you rely on first attack only. This also mean the team playing 2-3 defense will have more possessions and if it's able to score better against you than you against him, they win.
If they have better rebounders than you and you play M2M or 3-2, they will get a lot of offensive rebounds and second chances and thus offsetting the advantage you have against their defense.
That's why I chose FCP, because I have a team with good offensive flow and especially Handling. Steals are not that much of a problem because I have a better defense than offense, so even if they have more possessions, they will not score more than me. Also my off.rebounds and their steals will probably cancel each other. FCP is a really horrid offense and worse than 2-3 in most cases.