I start considering defense after I buy Surge of Power, as written in the Situational description. This includes upgrades, so I don't just buy Debuff Reducer then grab Point Blank, but instead I get both Debuff Reducer and Remover (if I need it) before continuing in Core. Some items are there for alternate playstyles. I don't typically use Restorative Shot, Decay, Torment Pulse, etc., but I don't think they're bad options to use either, which is why I leave them for people who prefer them over other items in Lane or Core.