Your take is 100% correct, but we still opted to use Ethereum Gas units as our "emissions factor" because it represents useage of and relative benefit from the Ethereum network.
We are interested in raising money for carbon offsets, so if we ask the question of "who pays?" it wouldn't be fair to place the burden on miners when all users benefit from the security and stability that comes from mining.
I'd eventually like to develop a model that allocates emissions based on "unit of time held" which is a more accurate allegory for 'benefit' for speculative assets like Bitcoin (if we are honest about Bitcoin's purpose), and because of the macroeconomic reasons you mentioned.
It's an interesting problem and discussion because unlike driving a car or eating meat, simply reducing consumption won't fix the problem, and yet we would all agree heavy users or benefactors of the network should bear more of the burden.