They are cool but always the last to arrive at the attack.

I could increase their speed, especially the later tier enemies. Thanks for the feedback

Make sense that a tank unit is more slow than other, I suggest u more than make it more faster, to do some "rush to the wall" tests and take some conclusion about right stats. Let's say that we can have walls is divided in 3 combinable category and 3 tier: ammo, laser, fire damage and weak medium heavy quantity of turrets. It's a good start for make tests.

If against a heavy full of turrets wall is normal that enemies will be destroyed easily, if armored units will be faster than normal biters but more armored is like that evolution will spawn enemies of upper tiers earlier, because ok...yes, a tank should be in the front line, but biters are monsters that don't know the concept of formation, I think what this mod want make is an new unit that is more resilient, with pro and con of it.

This foreword is for say that it's ok that the armored biters will be in the rear part of group wave of biters, the speed should be enough for follow the group but not for be in the front part.

Also I suggest u to play with damage resistances, like the fire damage is that for remove the quantities, armored unit should be more resistent of area damages.

Also u can play with spawning rates, if a tank unit is more resilient and an entire group of it is unbalanced, probably make it sort of 3:1 or 6:1 biters/armored, could help to make a sort of balancing.

I think, vanilla Factorio's turrets behavior is to attack the closest enemy first and then stick to it. So imo a tank unit would have to be fast to arrive at the defense line first, have a hughe ammount of health and little or no attack power. This way, I think, it would suck up all the damage dealt from the turrets in it's vicinity and give other units protection until it is destroyed but at the same time can not go on a single unit rampage.