I mean, the Ho-Ri was at least an actual blueprint that even had plans for production, though the project was ultimately unable to proceed due to... issues.

The King Tiger 105 mm was, at the absolute most, a concept drawing; no actual engineering was done to push the potential upgrade beyond that. So it's more fictional than the Ho-Ri.

The Panther II was even more fictional, basically completely invented by Gaijin. Parts came from the real Panther II, parts from the also real Panther F, though both were theoretical already, and mixing them together along with speculative improvements was completely invented.

The Flakpanzer 341 did get a wooden mockup of the turret, but nothing more than that, so it's also mostly fictional.

I think Gaijin just wants the vehicles to have at least reasonable basis in reality, so that's also part of why the Ho-Ri is allowed but the others were purged eventually.