In theory, that's correct. The problem is that to do it correctly requires certain personnel in terms of length/quickness, and there just aren't enough of those kind of players in the league for every team to play that way. You can point to GS, Houston, Boston, and the Cavs as being successful teams that switched, but that's a bit of a chicken/egg situation. Were they good because they switched, or were they good because they had sufficiently talented players to play that kind of switching defense? And are those players who can switch also good enough on the offensive end to give you a strong offensive?
It's tough to find guys like that.
So unless you're one of those teams fortunate enough guys capable of switching who also are as good as they need to be offensively and otherwise...what do you do? Do you keep trying to switch a lot because "that's what good teams do", or do you get more creative and use the players you do have to put together the best defense possible, even if there isn't as much switching as is ideal?
At some point, if you don't have the players to fit the best "scheme", then it's no longer the best scheme for your team.