It is more like cost to compensate it only have 3 tires instead of 4.
No, it isn't. It unlocks one expensive unit for purchase (Either a 500/185 comet or a 540/150 churchill). It's there to offer tech diversity since everyone else has far more options about how they choose to tech and you choose between supergrenades + super speed or heavy engineers. Heavy Engineers are good, but if you had to pay munitions for the upgrade it would be much less appealing to go Anvil spec. It's not comparable to a Tier 4 at all.
At the end of the day, there's a billion ways to counter a strict anti-infantry unit in that stage of the game. Yeah, they're really good against other infantry in a shoot out, but that's about it. They're vulnerable to tanks, indirect fire, grenades or even suppression since they can't move fast enough to flank machine gun teams. They're a defensive unit in a defensive specialization on a defensive unit. 200/50 is already a pretty hefty cost for what it gives. That's more than half the cost of a centaur or almost half of a Cromwell, which could have a much bigger impact.