I haven’t missed anything. The graphic just shows that:
a) when you have two buckets, spammers will abuse both.
b) if you close one, they’ll switch to the other, so you need to close both.
c) fees can’t outprice spam, bc there’s infinite demand for free data storage
> our blocks will be systematically full of monetary transaction because of adoption
Good, that’s the whole point of the debate: save the 36% space used by spam to accommodate more financial transactions. In this regard BIP110 is a de facto scaling solution.