Great material. Although a pruned node as "castrated" is a fairly strong position. Pruned nodes make snapshots and never have to do IBD again. The white paper included pruning for a reason and in the long, long run all nodes will eventually be pruned. Electrum servers and lightning channels are "extensions to" not "features of" bitcoin. Totally optional by providing enhancements and features such as block explorers and light client connectivity, but not a requirement.