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Correct me if I'm wrong but general grievous didn't posses any force abilities, being almost 100% robot, but he still could wipe the floor with any jedi 1v1 or even 1v5 in lightsaber duel. His only weakness was to superb force users like Mace Windu.
So, with the right training and cybernetic enhancements, even if they don't have any force powers, anyone could wield a lightsaber and win against a force user.
On that note, would you allow a character similar to general grievous to play as?
KOTOR II's central message was basically "Jedi are very easy to kill if you know what you're doing, and the Force is not all-powerful", which I'm sure Grievous was partially inspired by. That being said the guy was personally trained by Count Dooku and probably had millions of credits sunk into his cybernetic capabilities alone. I don't think any character with that level of training would be able to fit with a semblance of realistic balance into the RP, and would also have a huge bounty on their head for killing that many Jedi/Sith. A group attempting to maintain a degree of covertness will likely not want a war criminal with them; for example, I politely refuse Joseph Kony's offers to join me and my buddies on a road trip.
Cybernetic enhancements are not out of the realm of possibility, but as with about anything in this RP, it should have realistic and fleshed-out (no pun intended) drawbacks. My character is a physically and psychically powerful individual with great skill at healing, but is aging, has very limited knowlege of the universe at large, is not inclined towards violence, has no formal training, and has language issues. She has her uses, but needs the rest of the crew in order to round out her weaknesses and capitalize on her strengths. General Grievous doesn't need anyone else because he can turn into a blender and carve up anything in his path. As a crew of smugglers, some muscle is ideal, but the captain probably isn't looking for a Jedi-killer for hire - what would be more useful is someone who can open locks, someone who knows a guy, etc, etc.
There is potential for a Jedi Killer character, but it would be more in line as someone from KOTOR II such as
as opposed to General Grievous. The former has uses and versatility on a smuggler's crew; the latter is kind of a one-trick pony that can't really be balanced.