Pershing will most likely be supported by a stock Jackson and infantry that can all be upgraded with bazookas. It is a valid reason why it is as "heavy" as it is.
And Jagdtiger and Elefant and KT will be supported by either pzgrens or obers or some other elite infantry. Or supported by cheap Stugs or JP4s. The argument doesn't really stand.
If you get a pershing and a jackson and infantry with zooks, you can easily lose to 2x shrecks and upgraded infantry. Unless the enemy is braindead and decides to spam P4s vs that.