Although the Eternal Sun Peak has many Mind Cultivators or Manipulators, they were mostly at the Brass Tier with a handful of Silver Tier…
As for Gold Tier Manipulators, they normally venture out of their Peak when they reached this level. They could be everywhere training their mind and perfecting their combat style with their Automatons with real battle experience.
It is said that there is a huge chasm between the Silver and Gold Tier so the latter was quite special and had plenty of privileges they can all enjoy.
This is the reason why Vivian couldn't send Gold Tier Manipulators to accompany Vincent and his team. As for sending Silver Tiers, it didn't come to their mind since Joran will just easily destroy them. Silver Automatons doesn't have the toughness and complexity that Gold Automatons has.
Nevertheless, Vivian allowed Nerissa to accompany Vincent's team.