If you try to stabilize footage with a flat profile ( like S-Log2/3) you have to increase contrast and color before the stabilizer in the filter chain. This is not possible with the Vegas internal Media FX stabilizer, which acts as the first part of the filter chain.
Mercalli can be used an Event FX and thereby is much more flexible and leads to better results.
But work is going on to improve the new Vegas internal stabilizer. I think it is too early to judge.