I definitely don't think a 2-3 zone should be used as the default defence. And I definitely don't think it is useful in all circumstances, all I'm saying is there are times when a 2-3 zone can and should be used effectively.
For example in my latest cup match, I played Run and Gun in my 2 league matches prior to the cup game to make my opponent play 3-2 zone, and in the cup game I switched to look inside. I also played a 2-3 zone in the cup game because I had a look at my opponent and knew that when he plays push the ball, his inside scoring is much higher than his outside scoring. So I played a 2-3 zone. He had an 80k center, which is more than my entire teams salary put together. If I played man to man then my defence wouldn't have been high enough to stop his inside scoring (he is ranked 200 more than me so he obviously has a much better team). However because I played a 2-3 zone, I managed to defend his strong inside scoring, and hence he would miss more from inside scoring, and because I was playing a 2-3 zone I also got more rebounds from these misses. This, in combination with the fact that he played a 3-2 zone against my Look Inside, means that I had the tactical advantage.
I think the case above is one where playing man to man would've lost me the game as his center would have completely smashed my center.