The easiest and quickest way that they can do for make up now is renaming the three heroes to Lord in normal games like the ranked, which can make them unspecific.
But I think people woud still against the heroes even if they were renamed. They should be replaced with something general, like the Wooden Ox for Shu, Guard Chariot for Wei, and Night Raider for Wu. Those units did be used in the history, and they can have good reasonable explanation for their aura, e.g. the Wooden Ox can heal units as it was a mobile device that transport supplies. As general units, you can reasonably train them without the limit of 1.
More my two cents for the 3K: Move on and make Three Kingdoms more accurate and balanced