Yeah, I totally see your point and agree that the SBBS argument doesnt hold water from a security standpoint. I also appreciate security first viewpoint, but even from that viewpoint it should be security first and usability second rather than just security first. I do not believe we have reached the minimum requirements for usability and I believe the situation is dire enough to sacrifice some potential security threats (p2p message storage-relay system) and some of the academic beauty of MW (one-sided/non-interactive txs). In fact, I think a p2p message storage-relay system could be used to increase aggregation and other things that increase privacy/security, which further increases the trade-off benefits.
I am not sure if it is possible, but maybe the event of p2p relay DoS attacks, nodes could detect this and shut this system down and/or ban the malicious nodes (over and over if necessary). Maybe these comms could be over a different port or something. If it could DoS the whole network then it seems like that attack is possible with current comms too but we already either accept that or have sufficient mitigation measures in place.