Does "far more" refer to quantity or quality? One document at a higher classification level than Snowden released to one person would make this true. Misleading, but true.
Snowden doesn't say. My best guess is that he as angling for a pardon here, or some sort of deal where he gets probation.
After all, Petraeus was worse!
Good point,
The truth is that the damage done by disclosure of classified documents is highly speculative. It (damage) can be counted in terms of financial cost or national security cost. Both measures are still relative.
How much is the cost of a critical vulnerability in a weapon system? How much is the cost of a lost agent who was compromised by a leak? The net result of asking these kinds of questions would be needed to determine who did the worst disclosing. Otherwise the question is meaningless.