Not necessarily a waste. Of course with 25 piercing and 50 armor it's a waste. But with 45 and 50 it isn't. Keep in mind that it's rare to see the theoretical armour of a division template in the field. Be it losses or older equipment, it fluctuates quite heavily, especially in longer battles. I've had many situations where tanks started with armour advantage but started getting pierced after couple days.
Myzael is quite right. I've seen it plenty of times, too.
I've also seen something far more distressing (for my opponent, anyway) when using heavy tank destroyers.
In two games as the Soviet Union, I saw German panzer divisions start a battle against my specialized tank destroyer divisions. They were being pierced on day 1, but otherwise were doing okay. But by day 3,
some of the panzer divisions had lost the ability to pierce my tank destroyers.
The losses in armor cut their piercing down to the point that they were simply unable to pierce my tank destroyer divisions. It's not like I designed them to be space marines, but losing even 50 tanks in a panzer division can seriously damage unit stats.
This leads to the other reason to use tank destroyers: stacking hard attack. Yes, you need piercing, but novice players often overlook the value of hard attack in hurting the ORG and strength of panzer formations. And with heavy tank destroyers, you can stack some hard attack, even more so if you pick the heavy tank designer and invest XP into the tank destroyer gun.
