The steam tanks currently are pretty hard unit to counter for some factions, especially the ones that lack the stronger AP single entities/monstrous cav/arty.

Maybe a good solution to this and also something that could raise the skill required to use for the steam tank would be to introduce an attribute called directional armor.

How this would work? 

A steam tank would have 100% armor from the front, 75% from the sides and 50% from the back. Possibly, the unit would need a slight overall armor buff (to the 180) to make it not a straight disadvantage; this type of change would allow you to counter steam tank kite with cav attacking it from behind; with skirmishers shooting at it's back + ranged infantry attacking from multiple sides could be a bit more effective.

As for the other attributes that could be helpful:

1) Battle hardened

- unit does not recieve morale penalties when flanked; possibly also when it's losing combat/facing stronger enemies (latter 2 only if it's not strong enough on it's own)

2) Oath of defense

- unit recieves improved melee stats and discipline when it's near general unit

3) Hardy and very hardy

- Stamina loss decreased by 25%/50%. Fatigue recovery improved.

4) Machine

- unit does not become slower and it does not lose armor because of fatigue (engines don't get tired; armor plates are static so there is no skilled armor usage involved here too)

5) Determination

- Gain improved melee stats based on the amount of enemy units nearby

6) Skilled at dodging 

- unit may completely avoid normal melee or missle attack once per x seconds, if it's not at very low discipline or fatigue; it's based on random chance (10 - 30%)

7) Enrage

- Gain improved melee stats the more nearby friendly entities die

8) Mage hunter

- When a spellcaster is very close, gain better speed and weapon strength

9) Counter - spell 

- This attribute decreases spell mastery of nearby mages

10) Tough

- Unit recieves less damage when it's attacked with projectiles/melee made by non hero small entities (that also aren't arty)

11) Easily motivated

- Nearby presence of general/hero/unit with encourage attribute gives 200% leadership buff

12) Hunt them down!

- Boost to the melee or ranged damage towards low leadership/routing units

13) Images of terror

- Cause leadership debuff that is growing bigger as there is more units/or enemy entities near you (simliar to boundless cruelty on Zhatan, but with bigger effect; or it grows more based on number of enemy SEM + heroes nearby)

14) Hates skaven/undead/greenskins/dwarfs/elves/ogres etc.

- A small buff to discipline/melee stats when unit is facing their hated enemy.

15) Adrenaline rush

- A presence of large unit nearby gives speed boost 

16) Sacrificial bond

- whenenver a nearby hero or lord recieves damage, a portion of damage is transferred to this unit (giving the lord/hero a protection of sorts, since they recieve less damage and the other unit recieves it instead)

17) Aura of tiredness

- increases amount of vigour lost by enemy units either in melee with something with this attribute or near it

18) Vigour steal

- make enemies lose x % of vigour per sec, like 0,1% meanwhile gain 0,1% vigour; possibly melee stat only

19) Lifeforce consumption

- recieve x % of damage dealt back as a healing; possibly decrease enemy heal cap when you spend time with them in melee