The biggest problem I had with "Tim Wayne" aside from the fact that the old Tim would never drop his dad's name like that. He loved Jack Drake. But the bigger problem was that the "Tim Wayne" didn't roll off the tongue. It just doesn't sound right (neither would "Dick Wayne"). When most people name their babies they usually go with a name that works well with their surname.
And of Bruce's legally adoptive sons, the only one I could have seen taken the Wayne name was Jason - who really never had a father except Bruce. Yet he's still "Jason Todd".