We are all addicts and we are all greedy, more or less... I guess everything depends on the moment. Addiction and greediness can cause problems, but they are part of us, if we overdoing something because we love doing it it's addiction, and if we wish to get more out of something it's greediness. As I said, both can be problematic, but not necessarily. We can control our gambling habits and limit our spending on gambling, in that way even if we lose because we were too greedy it's not a big deal.
So I don't think that we can measure which one is more disastrous. Firstly because they don't need to be bad, and secondly if we have some control over our funds for gambling both can be controlled and will not create any problems.
That is a dumb statement, we are not all addicts in any capacity. Addiction is psychological phenomenon in which a person just can't stop engaging in a particular behavior, even in the face of the dire consequences. This includes attributes like bad impulse control, extreme craving, numbness etc - all applicable to the behavior in question. Addicts literally have different brain structures compositions than normal people. The term implies a certain threshold of intensity and some prerequisite behaviors, where we can start attributing it to people. As far as I know, normal people don't engage in this kind of behavior, engaging in impulsive behavior spasmodically or in some minor capacity doesn't take someone to vicinity of addiction. Its a very specific word that is used for a dangerous behavior. Using it randomly like this is silly.
It would be like saying everybody is schizophrenic, more or less... Because everybody can be delusional from time to time. But of course that would be make no sense, that term is to used for a specific intensity and pattern of behaviors. The same is true for addiction.