Not true. It pulls chakra in gradually, not all at once. If a Preta user grabs a person and starts siphoning in their chakra, and the person did nothing to stop it, the chakra would just keep flowing into the Preta user until the person's chakra is depleted.
When it comes to the barrier, when a jutsu makes contact with the barrier, it's gradually absorbed. One end of the Rasengan hit the barrier, and was gradually absorbed into it. But the entire thing was still absorbed. Same for a TBB. It can't bypass the barrier because anything made of chakra is absorbed into the barrier. A TBB hits the barrier, and its movement is halted and it's slowly sucked into and absorbed by the barrier. It won't happen instantly all at once, but all of the TBB will still be absorbed. If the TBB explodes, the explosion will affect the area around the barrier, but nothing inside of the barrier will be affected because the explosion has to pass through the barrier first, which is impossible because any ounce of the explosion that touches the barrier will be absorbed.