Sadly, just about anyone is an upgrade over Nicholls. If you look at the history of the conference in each sport, you will always see the number of championships in each sport. There are always dynasties, like us in volleyball, La Tech and La-Mo in men's basketball and SFA in women's basketball. In baseball you see a few teams like Lamar and Texas State at the top.
Nicholls on the otherhand rarely is in the top two-thirds of any championship list. McNeese is usually competitive in the team sports. UL-M and UL-La are a McNeese equivalent, but there is nothing in the Belt like a Nicholls. In fact, in many ways, the SLC is a good conference if you look at the top tier, but it is the bottom tier that brings it up. In baseball, as an example, Lamar was clearly in the lower half, but since they had a good showing against non-conference opponents, brought everyone else up (they are rated the fifth best conference team in the RPI index). That doesn't happen in the other sports.
The SBC as a whole is better than the SLC. The top tier, however is only marginal.
The ironic thing is that if every SLC team stayed put, the conference would be at the same level or higher than the Sun Belt. Of course, it may have been the move-ups that allowed some of these teams to get better. However, as a precursor of things to come, the Southland dropping to 1-AA in football precipitated all of these moves. UL-La moved up right away. UL-M, UNT, La Tech, Ark St, Troy and now Tx St and UTSA all left the SLC so they could play in 1-A. One more school and the former SLC schools could make a complete conference.
But yes, you can still call them the Slum Belt. With the dissolution of the WAC, they are still likely to be the worst conference of the 1-A's. However, since they have stayed relatively intact, they should at least be better overall. We know the Big East, Mountain West, C-USA and most certainly the WAC, if there is going to be a WAC in football, got worse. That in and of itself is huge for the Belt.