I played plenty of games as Assasin tank + Sorc healer (brother and I) + 2 randoms. Our basic strategy was I sprint to the ball, he goes top left or right and grips me up once the fire is down. After that (my sprint is down, his is up) he crosses the fire pit and I pass to him. He sprint jumps over the edge to land and cap total time ~15-20 seconds. I'll outline how to stop this strategy.
1. Wreck the Sin with the ball early (only works with stun+focus).
2. Don't let the Sorc stand up on the ledge. This can be done by one person.
3. Actually leave someone on defense at goal with a knockback (Jugg works very well, PT too).
4. If the Sin tank is using Cloak to cross a fire pit, many roots will still work including Sniper, and Warrior roots (anything that does white damage + roots, as well as charge roots).
As a Marauder you should be on that Sorc as hard as you can, not much else you can do. Force choke over the fire is good too.