If there are a significant number of pruned nodes on the network will it impact network security?
Your points 1 &amp; 2 are both correct. The good news is the only time those old blocks get requested is by new nodes that are still bootstrapping and downloading the blockchain for the first time. As long as those old blocks are available and accessible somewhere, those new nodes will sync up just fine.
Another fact about pruned nodes is they are required to store at least the most recent 288 blocks. So if your node has only been offline for a day, you can still sync up from a pruned peer.