Edit: A DDoS against the Monero blockchain would the require the attacker to keep paying fees in order to maintain the blocksize at a given level.
I largely agree with your comments - the blocksize debate is not just limited to a simple technicality, it's a question for how Bitcoin can grow without pushing out many users/use cases that can't fit in under a high fee market.
To the point quoted above, how does this work when the attacker is also a large Monero miner. The fees they'd be paying would largely go to themselves, no?
There is still a loss with a miner spamming the network since they would only get their hash rate percent back. If they control say 5% of the hash rate they still have to pay the remaining 95%. In addition the would forgo the legitimate fee revenue and / or still have to pay the block penalty on over size blocks. So it would not be economically advantageous to spam the network. This however is not the case in Bitcoin where it can very advantageous for a miner to spam the network in the current situation of a fixed blocksize limit and close to full blocks. The miner spams the network in order to increase the overall fees against the fixed blocksize limit and can directly profit from this even with a small percentage of the hash rate.