True, Seraphine plays more like Lux, but I guess the defensive part would be the peel from the bonus movement speed and generous E target (shorter in exchange for hitting multiple people while Lux's Q is 2 seconds for 2 targets max.) and the conditional heal from W. Also, the augmenting of allies could be how the heal is multiplied based on number of allies present and how the E and R have greater power with allies. (https://leagueoflegends.fandom.com/wiki/Champion_classes/Controller#Enchanters). It's just that Seraphine, as a burst mage, can afford to augment and directly support her team while Lux is meant to burst squishies with great range with limited self-peel (especially if Q is on cooldown).