If you just said “flu kicks your ass more than the common cold” we’d be in agreement, since “common cold” means a mild non-specific viral infection, and “flu”

If you just said “flu kicks your ass more than the common cold” we’d be in agreement, since “common cold” means a mild non-specific viral infection, and “flu” means a severe non-specific viral infection. But once you arbitrarily declare somebody didn’t have flu if they weren’t sick for three or more days, or didn’t get a high enough fever, well then I don’t think that’s valid either in common usage or scientifically. Since you brought up people misusing terms, I think that’s a pretty valid response.