It should be noted that T1 and M6 heavies were both actual tanks manufactured in a few dozens. They were never sent overseas to fight, though and the programs were cancelled.
There is however another tier 8 heavy which saw extensive combat – the Tiger II. VK45 and Maus were prototypes, however, which leaves 1/2 of the German heavies as “real” tanks.
Of the entire IS series, only IS-4 was a prototype, all the rest were “real” (the IS-7 being renamed and seeing production as the T10) and even saw combat (IS1/IS2 unquestionably, and possibly IS-3). Before this, the KV line is a mixed bag, KV-1, KV-2 and KV-1S were all real tanks that saw combat, KV-3, KV-5 and KV-13 were prototypes, however.
Tthe German VKxxxx tanks, the tier 7-10 US heavies and half the US mediums create the impression that the game is full of fictional tanks. But the majority of the tanks, some of which may be obscure (and wait till we get the French stuff!), they are no less “real” than the icons that stand out in public memory.
It should also be noted that with the reformation of the US medium line, effectively just one prototype will remain on the tree (T20). On the high end, the Pershing and Patton were both real tanks that saw combat, and on the low end the M3 Lee and the Shermans are iconic vehicles as well.
When it comes to Tank Destroyers, the vast majority of what we have in the game were real vehicles that saw actual combat. All the Russian TDs from the SU-76 to ISU-152 were production vehicles that saw combat. Only AT-1 and Object 704 stand out. For the Germans it’s even better, as every single one of their TDs in the game was an actual machine that saw combat. From the lowly Panzerjager I to the JagdTiger.
With artillery one has a point however when we move beyond tier 5. But honestly I wish it weren’t in the game at all. Not being “real” is the least of my problems with the class.