And a 160 fuel ultra-niche unit that cannot defend itself against anything isn't a significant investment?
The Panther is zero risk compared to the Sturmtiger. If you get a Panther and he doesn't get any Tanks, you just have the DPS of LMG Grenadiers rolling around protected by 320 armour and 800 health. If you get a Sturmtiger and he does go for Tanks, the Sturmtiger cannot defend itself. It sounds like you Schreck Blob so obviously that's less of a concern. The point is a bad Sturmtiger can lose you the game, but a bad Panther simply means you do less damage than you could have.
Nobody is saying that a Sturmtiger is always a good choice, and that it cannot be a bad investment. But a Panther can be a dumb investment as well if your getting it to counter infantry which is not it's main purpose.
For example, if I'm facing a lot of medium armor it makes sense to get a Jadgpanzer if I have the HQ, if I don't then I get a Panther. Similarly, if I'm facing massive amounts of support weapons and I have a Mechanized HQ I can get a stuka, but If I don't I can get a sturmtiger. See how this works out?
And again this is entirely dependent on the game mode. The Panther shines greatly in 1's and 2's because it's typically going 1 on 1 or 1 on 2 versus enemy armor. In 3's and 4's the amount of tanks your facing ramps up and so does the amount of tank destroyers. You also have to deal with a lot more blobs in 3's and 4's as well which makes the Sturmtiger more useful more often.
I think this disagreement is happening because we are all talking about different game modes, I honestly don't think a Panther is -always- a good investment, it is mostof the time but if your facing a skilled player the Panther's value greatly reduces if it's not fighting what it should be.