A few tips, 1. Try and scale back your map: large areas or over scaled rooms can lead to sniper being favored heavily throughout your map. Try and work on making a balance of small and large areas with plenty of cover. Slower classes like Heavy will not like playing in large areas due to how long it takes to make it to the objectives and the constant risk of Sniper giving them a one way trip back to the respawn room. 2. try working on some test maps to get the hang of props, gameplay systems, gameplay logic, and level design to perfect your technique. 3. Payload tracks are arduous to place, it isn't as easy as playing with wooden trains or Lego bricks. It takes Time and effort to learn how to perfectly lay out your tracks, which even I myself am trying to still perfect, so keep practicing and remember that Payload tracks cannot turn sharp 90 degree angles, try working on learning to make curves with basic straight tracks and curved prop tracks.
I look forward to see you improve in the future, so keep at it!