Well some how you've lucked up because I've had nothing but problem since coming back and using TS12. Things that worked become broken mysteriously, content from DLS requires content from some other site, ect.
I love backwards compatibility when it works but things are so bad with content being hack upgraded from older versions of Trainz to work with newer versions and doing more harm. Maybe having making the process simple to re-export content but having a new system isn't always a bad thing, even if it's frustrating to begin again.
This also opens the door to newer things added because they don't have to worry about will it work with old content. I recently started to play with RailWorks Train Sim and while it's no Trainz there are some cool things to like that I wish Trainz had. Lastly, you know it bad when people are still trying to run content from 04-06 version, like the Acela which was NEVER rebuilt by anyone or Landrvr1 or a number of other members who are no longer active.
I can see it how it can work while keeping it simple: Start a pool of common bogeys, select the best and just use them. Same for lights, and other commonly used items like couplers that will always be on DLS 3rd party shouldn't even need to re-create the wheel.
I can go on but I won't other users know about the frustrations and have experienced them.