XSUPREMEXSKILLZ
The Immortal Emperor
Exposure does nothing to raise or lower Valk/Sids. If all evidence shown in Valk's illustrious career isn't above the evidence we've seen of Sidious' illustrious career, logically Sidious is superior. As of Revan and even SWTOR people were perfectly logical in believing that Vitiate was sub-Plagueis/ROTS Sidious. Because there wasn't enough evidence at the time to point to Vitiate being inarguably superior till Ziost/KOTFE. However, Valk's start to finish is inferior to Sidious' based on the evidence that we have, IMO. At their absolute peaks we saw them both operate at, Sidious was more impressive from a combative, cosmological, and manipulative standpoint.
Like I said in another thread, though, I think a lot of that can be attributed to Valkorion being poorly written. Like, he goes from Sidious-level mastermind to getting ****ed by the Outlander and a holocron he made when he was 10 in an instant. Switched from nuanced to cookie-cutter so quickly.