This is the initial system we had, download a .zip file from a peer, then download the lasts remaining blocks. It had many downsides, like a) being centralized, b)zips can be use to attack, c) you only know if data is correct after downloading d) if somethings goes wrong, you have start all over again etc. PIBD is much more robust | secure | fast, but it could use some speed improvements.
Some of those improvements are just changing settings, other might have to do with the peer to peer messages itself or even the network socket, which is more challenging to work on.
See this thread for my investigation on fine-tuning and speeding up PIBD: