I have asked this multiple times, but maybe I wasn't clear enough.
You use Vault to understand what Group a player is in, this is incredibly limiting.
Support LuckPerms, there is absolutely no reason for anyone to use any other permission system in 2018.

1. Natively support luckperms, don't go through vault.
2. Check the Rank weight so you know what ranks are higher than others from Luckperms.
3. Use the LuckPerms track system to find out what track a user is on, so you know what rank they need to rank up next if they have multiple ranks.

Example 1:

STAFF
This rank is HIGHER but it not touched by autorank and is set manually.
Staff1
Staff2
Staff3

Normal Linear ranking
Autorank lets them rank up in, read from the luckperms paths.
Rank1
Rank2
Rank3

Example 2:

DONATOR.
This rank is higher and is set by BuyCraft, not to be touched by AutoRank.
Donator1
Donator2
Donator3

Normal Linear ranking
Autorank lets them rank up in, read from the luckperms paths.
Rank1
Rank2
Rank3

Example 3:

BUILDER.
This rank is higher and is set by Specific staff, not to be touched by AutoRank.
Builder1
Builder2
Builder3

Normal Linear ranking
Autorank lets them rank up in, read from the luckperms paths.
Rank1
Rank2
Rank3

LuckPerms recently had a massive new update with a completely new re-written developer API, maybe start with the new API as it will only be improved.
https://www.reddit.com/r/admincraft/comments/e2a3bh/luckperms_v5_beta_has_been_released_with_a_brand/