Actually, I've noticed that I've kinda pulled that phrase out of context.
His point was valid (about unit diversity), but still doesn't explains why Puma should be more cost efficient.
And he won't be able to.
Puma is armored car fitted with outdated, pre war gun.
M10 is actually armored vehicle fitted with actual anti tank gun made during the war.
Puma arrives earlier and is cheaper, its lower penetration at long range is the only thing keeping it from becoming op, up close its dangerous to all tanks but heaviest ones, it has smoke, it has TWP and great scaling which boosts its damage up to normal TD level of 160.
That is like comparing T34 to Tiger and complaining that T34 is weaker.