Hello,
please get rid of individual and hidden fighter thrall (and pet) stats.
For example health:
 Overall health is influenced by vitality, start health, health bonus multiplier (hidden and messy), and vitality % per level.
If you make a bad T3 bearer you may end up with 25 vitality and 14k health.
If you then make a good T4 (perks, vitality per level % and faction) you may end up with 45 vitality 8k health.
= messy
For example damage:
 Overall damage is influenced by strength, start strength, damage multiplier ranging von 0.5 to 2.5 (hidden), damage multiplier per strength (hidden), the weapon damage, and strength % per level.
How do we all know, berserkers do great damage? From the data  miners … That is not how stats in games should work.
Streamline this!
The player should know with a glimpse how good a thrall is and why.
Suggestion:
(Let’s assume, a thrall can get up to ~50 (65 for strength) of an attribute by perks (up to ~20) levels (up to ~20) and armor → if you are extremely lucky)

Vitality of thralls ranges from 5 to 50 at the start, depending on tier and faction.

Health is vitality * 100  and nothing else.

This way the best thralls may end up with good perks, vitality armor, and level 20 @ ~10k health.

Damage multiplier is always 1.

Damage is based on strength/accuracy and weapon  and nothing else.

Strength and accuracy of thralls range from 15 (bearers) to 35 at the start, depending on class, tier, and faction.

Strength and accuracy always add 2% to the damage multiplier.
This way the best thralls may end up at ~100 strength(~85acc) which is equal to 3 times the damage and not too far from cimmerian berserk (2.24 + strength bonus) 
Survival of thralls ranges from 25 to 25 based on their tier and faction.

Survival adds a 2% damage reduction of dots.

This way, the worst thralls will take 50% more damage of dots while the best ones may even get immune, making survival an important attribute.

Agility of thralls ranges from 0 to 40 based on tier and faction.

Base armor of thralls is based on Agility and nothing else.

Agility adds 10 to the thralls armor. (same as currently)

This way the best thralls will end up at 900 armor.
In this model, the base values of a thrall consist of class, tier, and faction.
The formula for base values is for the dev, not the players, and can thus be more complicated.
For example, this could work:
Value = class bonus + factionbonus * tier * 0.75 (round up)
Let’s say archers get + 10 accuracy, + 5 agility, warriors get + 10 strength, + 5 vitality, bearers get + 10 vitality, +5 survival, 15 strength/accuracy and finally dancers get + 10 agility, + 5 survival.
Let’s also say Black Hands get a bonus of 1 strength, 4 vitality, 2 agility, 8 accuracy, and 5 survival.
A T3 Black Hand archer then had on the start:
1.06 melee damage multiplier
1.56 ranged damage multiplier
100 armor
900 health
23 % damage reduction of dots.
Let’s say the Forgotten Tribe members get 8 strength, 13 vitality, 0 agility, 0 accuracy, 0 survival.
A Berserker would then start with:
1.68 melee damage multiplier
1.0 ranged damage multiplier
0 armor
4400 health
0% damage reduction.
All the values without much tweaking, and both would scale better with the new system. While high vitality/strength thralls would still be the best overall companions, you could actually make a bigger variety of useful thralls from other factions.
Finetuning would just need to balance faction bonuses a few points up or down.
Okay, that is all I wanted to say for now  thank you for reading!
Korahan