I am gonna be a little rude, sorry in advance
I don't think YOU understand how the game works.
1. "There is no injurable unit that can be built with mithril"
What do you mean? If you mean that DWARFS have no such unit, then thanks for the enlightenment.
I am playing dwarfs since August last year, and didn't now that
2. Let me explain how it actually works now for Dwarf race, so others can take some good advice and avoid the wrong way.
We are talking about garrison now, and what is the best way to build it.
If you put no-injury troops on your wall - they will eventually become a honor food for a bigger player. It is even more attractive to attack such garrison, because in the end-game most players are honor hunters, they don't need basic or rare resources so far. I don't, for example.
It is better to build a dwarf garrison with gold engineers + gold snipers (deadeyes), because gold engineers are tough enough to hold the enemy army long enough until deadeyes spend all ammo.
Plus, the biggest advantage is that they can be healed in a hospital.
You spend crystals + blood diamonds.
You are left with unspent mithrill - but if you PVP and siege a lot - you will need some stock of mithrill to replenish lost mechs (silver or gold).
You shouldn't put gold/silver mechs in your garrison because some of them can be killed even with bronze+Jac (especially high level hero and troops). And almost all of them will be dead if you are attacked with gold army.
I don't even mention gold tanks in garrison, because this is the most ridiculous way to spend blood diamonds.
Most people think that they have to use silver/gold mechs because they are more tanky.
And they are, I agree. However, you don't need their "tankyness" because your main DPS on the wall has ammo limit. And it is wasted almost equally with gold engineers start to die. But mechs hold little longer - however there is no sense because DPS loses its impact wit no ammo.
You don't need to put gold bombardiers on your wall, because they are useless without Fire Off ability.
Silver troops are useless on any garrison.
Many people combine their castles and defend each other, so human tanks, that can be healed, are back-defended with gold snipers. Or any other combo. Rakkans have a huge buff if they defend someone.
Currently garrison automatic layouts are mess and chaos, and we can't operate our troops on the wall and on the ground, we can't make formations that can be strongest and make some good damage to the enemy army.
So to sum up all the above said:
Don't make the mistake and use only none-mech units on your walls.
If you put mechs or tanks there - it is your fault and dwarf players should not cry. At least they should regret about being stupid.
High level players don't care about you wall at all.
So don't waste your mithrill.
Any offense is always > defense in the end.
So logically it is better to go for healing troops instead of making new and use thousands of rare resource - just to be destroyed once again.
I really hope that people will take this into consideration
P.S. You can no agree with me, but the truth will not suffer or change from that.