When considering he built the largest public works (baths of Caracalla) and granted citizenship to all free Romans in the empire, it seems odd that he’s portrayed as an “evil tyrant”.
“Geta's brother Caracalla acted as Severus' second-in-command, and administrative and bureaucratic duties were Geta's responsibility.” link
Is it plausible this was due to how Caracalla followed in his father’s footsteps and ignored the senate and only gave attention to the army while Geta did the opposite? I would assume the historians at the time would have aligned philosophically with the senate and would have seen the actions of Septimius & Caracalla as atrocious & diabolical.