It’s not about 7TB vs 22 TB or $1m vs $10m. These are back of the envelop calculations anyway. For one, attack cost could likely be significantly lower than described as many people simply sit on the free hardware.

It’s about the fundamental issue of super cheap and super effective spamming resulting from the “no fees” assumption. Even w/o the actual attack, the issue will manifest itself organically some years from now, assuming exploding popularity.

PS And no, one cannot do much about the “nodes” that spam, as there is an infinite number of easy IP-hiding solutions.