I understand why you might think that, but a difference in difficulty doesn't always have to mean a higher ilvl is required. Savage will have more in the way of challenges for people to overcome. The following is from the last
Live Letter
Groups joining Another Sil’dihn Subterrane with less than 4 members will be matched together. In exchange for the usual methods of resurrection being unavailable, each member will be able to use Variant Raise II a certain number of times, though all other Variant Actions will also be unavailable. Fulfilling certain requirements will recover Variant Raise II’s limited number of uses. Enemies that were defeated will not revive after your whole party is KO’d. Even common enemies will feature a slew of different attacks, so you may want to consider the priority of which ones to defeat first.
As for Another Sil’dihn Subterrane (Savage), joining will require a pre-formed party of four players. All methods of resurrection and Variant Actions will be unavailable, and all defeated enemies will revive when your party is KO’d. Enemies also won’t telegraph any of their attacks, you’ll need to memorize them from Another Sil’dihn Subterrane. Furthermore, they’ll become much stronger after certain period, so you’ll need to clear the dungeon within a certain time limit!