The problem which is ignored is that the US tank destroyer doctrine did not evolve in a vacuum. It evolved in response to the battlefield situations of 1940, when the Battle of France stunned American military observers and left them scrambling to figure out a doctrinal response to the idea of a rapid armored breakthrough as had happened at Sedan. The Americans designed their tank destroyers to provide units with the operational mobility to be able to plug exactly such a hole, and to be able to stop the catastrophe of 1940 from happening to them. Based on what happened in 1940, its an entirely reasonable idea and responds well to the disaster that the French faced, and for an army which had no experience in anti-tank warfare was hardly a bad idea.
Proposals for heavy tanks ignore this, because in addition to the objective shortcomings that incorporating heavy tanks into the US army would create, they don't match to an effective program of defending against the feared breakthrough and mobile war which the US was designing its forces to face in 1940. What would a heavy tank unit do do when a German tank corps breaks through at a specific section of the front and marauds into the rear areas, forming a giant encirclement and annihilating friendly forces? Trundle forwards slowly into combat after the battle was already over, just like how French forces had taken too long to move up themselves? More towed anti-tank guns, split up in penny packets along the front? Surely the French had shown that that was a bad idea, would be the response I am sure. What about more regular tanks? Well, the US army did that too - its armored division tables of organization had an absolutely ridiculous number of tanks in them, and it wasn't until later that they got a more effective and balanced schema.
The US army tank destroyers were logical for the situation they were designed against. Historically, they proved unnecessary, and only really got to be used in their intended role in stopping a massed enemy tank advance once, in North Africa (where they performed entirely decently at El Guettar), but the Americans are designing for what they had just seen happen in front of their eyes, the vaunted French army melt under a decisive armored thrust which they lacked the mobile reserves to respond to, and were writing up their doctrine and building their equipment to respond to exactly that sort of problem, not to what would happen in a relatively distant future which the Americans had no way of knowing would happen. An American force with a vast preponderance of armored forces advancing across Europe into an enemy sordidly equipped with their own armored units and incapable of conducting the same mobile war which it had a few years before is what we know happened, it had no reference to what Americans were planning their army to confront in 1940.
If you want to have a different armored doctrine for the Americans, you probably need a very different Battle of France that shows the value of other units and devalues that of mobile anti-tank forces. But that leaves many more butterflies on the world in all possibility than what sort of anti-tank doctrine the American army has, since the American army would probably never see a battle in Europe anyway with such butterflies.