So I have been seeing this lately, people reporting that Sackboy's level 3 is nerfed in the sense that the bubbles move faster, (4x faster in fact) and I've studied it a bit. I have played as Sackboy since his 1st nerf, and he is my only main. Here are my conclusions:
1. People are claiming that his level 3 was nerfed badly. The bubbles do move faster, but NOT 4x faster. This can become problematic because on stages like columbia, players get out of Sackboy's reach completely, and with the new speed his level 3 will become useless on the stages with no roof.
2. It is still possible to get 3 kills on a single person. 7 in FFA, 5 in 2v2, and 3 in 1v1. Before reading the forums, I hadn't even noticed the supposed nerf.
3. Lots of complaints have thankfully remained un-answered, such as the ridiculous ideas that people should not spawn in bubbles, and that the bubbles should not spawn on the ground. If they had addressed any of these, it would have been a TRUE nerf to Sackboy.
In conclusion, Sackboy mains do not worry. We may end up being robbed of at most 1 kill, but if you still know what you're doing, and use checkpoints to reach people on the other side of the stage, you can still net the 7 kills, albeit supposedly taking a bit more skill. This should not effect Sackboy too much. It's ridiculous that they even bothered nerfing it, and I have to say I'm very disappointed they even altered Sackboy at all, leaving his Jam Session with a useless AP gain, even though it was originally stated he is a keep-away character. Hopefully no more changes will be made. Sackboy has been hit hard enough.