Accidentally discovered a critical bug in SFM. I re-rendered this animation several times and each time it came out darker despite me trying to fix the lighting.
I had noticed this issue in several of my renders appearing darker when I rendered them which meant something was amiss. I thought it was purely color encoding but that's no longer the case.
After further testing I figured out that SFM's first viewport is not the one used in rendering. It's the second one. So it seems almost every SFM artist is actually running into this handicap and explains why almost every SFM artwork is so dark compared to every other 3D software.
The image I've included is a rare case. The light calculations have lead to the leafs in the forefront not receiving any light compared to the viewport image. You can also see the Blood Elf's skin is a bit brighter as well.
I'll have to new lighting to this animation for now.