I understood you. IIUC the different data manager vs data holder personas protect against your scenario. See image below. Your ddos would be occurring at the data manager level (DM)
The adversary would need to own one or more data manager nodes as well as the corresponding pmid storage nodes in order to benefit. IMO because of the random placement of nodes in the network, achieving this comes down to brute force probabilities. Note the layer of indirection between the data managers and the actual stored data.