May be I am reading the opposing arguments more, but isn't the block size being small affecting transactions speeds?
The confirmation speed is certainly affected, the transaction propagation speed remains the same at a few seconds.
nodes could share portions of the blockchain and unspent transactions
Sounds good, would never work. Bitcoin is built to be trustless. Unless you can find an implementation which nodes can store parts of it and still have it verifiable and diversed in terms of its difficulty to execute a DOS attack at a specific node to hinder the access to parts of Blockchain, it will never be possible.