Wet dry filters work fine, in fact they had a big part in helping the hobby evolve to where it is today (that and understanding lighting needs). A lot of people still use them with great results.
One of the problems with wet dry filters is channeling of the water. In order for it to work at 100% of its' capacity, all the balls have to be evenly wet, but water always takes the path of least resistance, so this is very difficult to achieve.
Once people started to use the live rock, we noticed a drop in nitrates, nitrites, and ammonia, and were able to keep more animals onctethought impossible. The DSB added even further to the process and increased the bio diversity once again.
A lot of people, myself included still use the wet dry filter as a sump. Just remove the bio balls and you have a perfect place for your skimmer, heater, etc and if you get real creative you can make part of it into a refugium.