No, that's not how 'wounds' are made. Wounds in the Force are formed when a great many lives are suddenly extinguished at the same time e.g. Malachor V & Alderaan. Stripping one of the Force doesn't make her a wound, just Forceless. And I think it was the fact that Traya taught Meetra to regain her powers that created the Force bond between them. But yeah, Force wounds are formed through multiple deaths and it was the Battle of Malachor V that caused Nihilus and Meetra to become wounds - as they were both present.
This means that Sion, as far as I am aware, is not a wound in the Force. Neither is Traya.
I'd classify Sion as more of a peversion of the Dark Side itself. As for Nihilus it seems that he can pretty much eat any living being touched by the force save for Meetra Surik and Visas Marr (Sion can survive it but he still gets drained) and they still needed Mandalore the Preserver to help them. So in any vs. thread unless your pitting Nihilus vs Abeloth or The Father, Son, or Daughter then its really a vs. thread with an inevitable outcome.
Sidious is the strongest, Vitiate is in the top5 too, but Nihilus is a living black hole that could eat them both.