I have both an r4 scorp and Silk. Silk benefits much more from the sig, Scorp at sig 1 has some cool extra utility. I use Silk much more because of BGs, and Scorp more in quests and act content. Scorpion has great DOT immunities and sneaky damage, and Silk hits like a truck with buff immunity. Scorp has a better synergy team, but absolutely doesn’t need it to be effective. Both are great and you can’t go wrong, but I’d lean towards Silk personally.
Both are fine unduped, especially if you’re not bg focused. Scorp covers a lot more ground and while he certainly doesn’t “NEED” synergies, he has a couple that make him absolutely crazy. Even without them he’s definitely the better questing champ tho.