Ok, time to dispell some myths.
This quote dismisses Nihilus' ability to consume planets as a rumor:
"Darth Nihilus was known as the Lord of Hunger and was known for his ability to literally consume the Force energy of his victims, which was known to sustain his own life energies. It was rumored that he could consume the Force energy of an entire planet." - Complete Encyclopedia, Nihilus, Darth
The same source makes it apparent that Nihilus used some sort of superweapon to obliterate planets or simply used old fashioned orbit bombardment:
"In the meantime, Nihilus led his Sith forces from his flagship, Ravager, drawing more and more power from worlds that he blasted into ruin".
For one thing Force drain cannot be used to "blast" things "into ruin", it is not a destructive power, it just sucks Force out of living beings leaving non-living objects completely in tact. Even in comics we see buildings being destroyed and surface ravaged. Either it was some weapon or a ritual-based Force power similar to Force Storm but not Force drain.
The only thing immune from Nihilus's drain, Canonically, is a Force Wound.
Nowhere it is canonically evidenced. The only time we ever see Nihilus using Force drain is on Meetra and the very same time he fails. And absolutely nowhere it says that she is immune because she is Force wound. Most people made logical conclusion that she resisted because she is wound, however, there is no proof that it was the case.
Moreover, within the same game there is proof that Exile is not immune to drain. Kreia uses her supposed to be "lesser" Force drain on her on Dantooine in one of the story branches and it works fine.
"It is a technique that is almost as old as the Sith themselves…it is a means of severing connections between life, the Force, and feeding upon the death it causes. It cannot be taught…it can only be gained through instinct, through experiencing its effects, first-hand."
―Kreia
This quote cannot be used as proof that it cannot be taught.
Plagueis said pretty much the same thing about lightning:
"
In order to summon and use lightning properly, you will someday have to be on the receiving end of its power, as a means of taking the energy inside yourself."
Numerous evidence shows that Plagueis' statement is wrong and that's why these kind of claims about techniques cannot be relied on.
Moreover, we have Krayt, who discovered Nihilus' holocron and learned this ability.
and Vitiate who is not a Force Wound like Nihilus - is screwed here.
You can't know it. Do you even realize that Force wound is just a phylosophical interpretation given by in-universe characters? No outside source whatsoever states Exile or Nihilus to be Force wound.
Vitiate experienced far larger Force disturbance, which resulted from his ritual. So, if Force wound thing is real, Vitiate supposed to be one of the most potent ones.