A pruned node is a full node. A full node is any node that is fully validating. A pruned node is fully validating;

"Full nodes download every block and transaction and check them against Bitcoin's consensus rules." (https://en.bitcoin.it/wiki/Full_node#Archival_Nodes)

Pruned nodes do just that.

The blockchain data structure means that once verified, you don't need to store old blocks. You only need the most recent blocks to verify new ones.

The nodes you're talking about, that store the entire blockchain, is called an archival node.

Anyway, encouraging people to install full nodes, pruned or not– which enforces the rules– improves Bitcoin's decentralization.[0]

[0]: https://bitcoin.org/en/bitcoin-core/features/validation