Using a blockchain while having a 51% attack advantage on said blockchain, is a contradiction in terms...
Sure thats a fair point...
I was just answering the "who pays" aspect, and before that the "why" aspect, and as I think I have shown the who and why and how are actually, upon looking , quite obvious.
The "who pays" question raises exactly this point. When those performing the security are monolithic in nature (either explicitly or by implication), you might as well use a private database.