Alright. You want the full explanation then
I hope you will agree with me on this: The key to winning fights and minimizing losses is to do all your battles in as few rounds as possible. The key to winning an era is to make sure your enemies die, while at the same time preserving as many of your own squads as possible.
For objective #1, minimizing losses, you want your battles to be done in 1 round. For a battle to be 1 round, there is absolutely no reason to have damage in your squad. They have 1 HP per 25 metal, and will do 0 damage per metal in a 1 rounded battle. Therefore in a 1 rounded battle they are inefficient both as armor as for dealing damage.
Then of course you might say that not all battles will be 1 round, and that many will be 2 round or more. This however is ignoring objective #2, preserving as many of your squads as possible. If you are constantly fighting battles where you lose more than you absolutely need to, you have a problem. This should be avoided at all costs. Therefore 1 round is always the objective and damage is obsolete. Armor is most efficient for HP, range is most efficient for doing damage.
Yes, your squads wins in an even fight. Wohoo. Tell me the last time you saw someone attacking and you thought: Heck, I'll just send the same amount of squads as he did!
Cheaper. Better. Stronger. Damage units, if have a lot of experience, will just absolutely annihalate in this build.
Cheaper: Yes. Better? Subjective. Stronger? How? You are sacrificing 7 range units in a squad to build 7 damage units.
What I find funnier about that comment is the last part though: If they have a lot of experience, damage units will annihilate in this build. Man, if range units have a lot of experience they will have range 4 or range 5. That's not a reason to go with damage at all, I would rather have my range get +1 than my damage. Because +1 range for damage still means they fire at the same time as the opposing range units.
A long story short.. If you are playing a world to WIN, as in to get rank 1 and nothing short of it, you will want to minimize armor loss and go for 1 round kills. Building damage units is obsolete in this case as the resources would be better spent on recruiting more range units leading to more damage in round 1 and therefore the ability to take on larger fights in 1 round. Going damage will work, but for damage to be efficient you need to do at least 3 round fights, since in round 2 range still has done more damage than damage. Doing round 3 fights consistently, which seems to be what you are aiming at otherwise you would not have this damage would mean unneeded losses and therefore a large increase in the amount of metal you will be spending on unit substitution.