I'd say most people have little respect for Vitiate because so much of what is attributed to the character owes to Sidious. Even the most recent development, with a reborn Vitiate striking out at a chaotic Galaxy with an advanced fleet originating from a top secret throne world.... All of that should sound uncomfortably familiar.
When you have a largely unexplored era and an opportunity to do something fairly unique with its big bad and instead imitate an established villain... A lot of people look at that as weak writing.