Howdy I’ll keep it sweet and brief
The Expertise System at a concept level is good, by how it is being so heavily focused on the RNG loot drop aspect, fails the system and I feel stunts the potential this fantastic idea the devs had, leading to it feeling of it being forced upon players to milk the current content.
What I would like to suggest instead is a style of progression that is familiar to everyone.
Expertise Progression Via activity.
Allow players to level up their character’s expertise in a more natural and immersive way.
Weapon Expertise, level it up by hitting rank 20 then using those weapons, the weapon exp now increasing the level of expertise the character has with that weapon
Again with armor, you could have it level up as the players move around, dodge and get hit.
Now regarding Item Drops
Iv always been a fan of how Dungeons and Dragons (Tabletop ftw) deals with Loot
Challenge rating of encounter = level of loot
Set the area loot tables of the most dangerous places to reward proportionate loot, reward the player’s effort with genuine tangible things.