Excuse me - but did you people have a look at the fighting location ? Dxun ? A jungle world ? When one of the combatants is Kar Vastor ?
I agree that Kar wouldn't be able to overcome Shimmra on a "neutral" ground but this is a jungle - his natural living space, the "source" of his powers. And physicaly the guy is a freaking monster. Mace himself (as far as I remember) was only staring at Kar's chest when the lor pelek was standing right in front of him which gives Kar almost the size of Shimmra. He is physically stronger then Mace when Mace was able to almost break the arm of a Korunai by just grabbing it - not with his strongest grip.
And now Kar and Shimmra are fighting in a jungle. Kar's powers exceed those of Mace Windu in this kind of enviroment. He can control plants as well as basically all kind of animals. That might turn out quite bad for Shimmra standing in a jungle crowded with all kind of deadly pretedators and plants - fighting against somebody who can control all of this.
I don't see Shimmra surviving the fight in this enviroment. Can be disturbing even for the supreme overlord to get hit by a tree, jumped by deadly creatures and then have an opponent with the own massive built attacking you who is armed with two weapons that can be used as shields, can cut virtually every other material and are able to withstand direct lightsaber hits. This will get pretty ugly for Shimmra, imho.
The fact that the jungle isn't Haruun Kal may hinder Kar a bit...and I'm pretty sure when Vong fight in dense foliage areas, they tend to simply obliterate the area.
Vong warriors alone are capable of cutting down packs of wild beasts and using devices to turn forests to cinders. Their Overlord would likely be capable of the same...Shim just needs a few blast bugs or Plasma eels