I remember a scene from the first season where Cecil has some experiments running on blood from Mark, hoping to find a weapon that could hurt/kill viltrumites.
Which is fking hillarious given Mark got beaten up and almost killed like once per episode.
They just want their cake an eat it: having viltrumites be both portrayed as world-conquering superbeings, while also telling a coming-of-age story with stakes, vulnerability and loss.
The real-world issue is cells don’t really have a “damaged but not dead” state because they are to fragile. In-world issue being that we clearly see cells getting destroyed (that’s what wounds are) and we even see viltrumites getting hurt and killed by regular weapons. So blunt force can totally kill them.