That is false.  Your node today doesn't 'trust' other nodes.  It downloads blocks and INDEPENDENTLY verifies them.  As of v0.10 you node will bootstrap by getting headers first and contacting multiple peers in parallel to download the chain.  If you only get x% of the chain from each peer then why does each peer need to have 100% of the chain.  Even if there was only a single node which had the full blockchain they can't modify the chain.  There attack would be limited to a denial of service (refuse to give you blocks when you ask).   Since you love to make false claims I will put it in black and white that I am not advocating a single node contain the full chain.  A DHT is a perfect data structure when nodes do not need the full dataset, and can't change the dataset.  That exactly describes the historical blockchain.

There is no reduction in security.  There is an increase in complexity but headers first and parallel block sync is already more complex.  The first client was very simple it contacted one peer and asked them for the full chain until it had a copy.  That worked when the network was very small but wouldn't work today.  The complexity of the interpeer communication will continue to increase over time even if the block size is never raised.