all but.. none but.. usage

I'm a bit confused with the usage of all but and none but:

1. "We are all but defenseless" – should mean we are definitely defenseless?
2. "None but misfortunes follow" – only misfortunes follow?

Were all but and none but used correctly here?

How do you use them correctly? There seems to be a contradiction.

The meaning of "all but" is "everything, except", or "almost". Therefore, "all but defenseless" means "everything except defenseless" or "almost defenseless".

Similarly, the meaning of "none but" is "nothing, except", or "only". Therefore, "none but misfortunes" means "nothing except misfortunes" or "only misfortunes".

They're used correctly in those sentences, and there's supposed to be a contrast between "all but" and "none but".