How can they even compare them? Nobody even suggested that COVID is similar to the other two. Cancer isn't even a virus and left to their own devices COVID is probably the less dangerous one.
Also cancer isn't just a single disease, there are multiple conditions that can lead to cancer and they all have different chances of survival.
Actually, you're wrong on that "Nobody even suggested that COVID is similar" remark. Nobody credible, or Nobody who knows what they're talking about and not lying, then sure, you're probably right. However antivaxers and disingenuous scientists absolutely have been doing that since covid was discovered.
Despite the retraction, bad actors don't care. They got a "study" and headline to confirm their beliefs, so they just act like retraction never happened and just lie lie lie. Echo chambers allows this to run unchecked, and then you have people believing they're equal.