Spectral walk and corrupt boon are invaluable. Spectral Walk gives necros the mobility they need in WvW. Corrupt boon serves as a disable which gives you the edge over who you’re fighting. In larger and clustered fights, you may remove spectral walk for epidemic. Corrupt boon + epidemic is extremely underrated. Well of corruption only removes 1 boon per pulse and that’s why I use corrupt boon. For the 3rd utility, you might want to pick well of darkness or well of suffering depending on what build you’re using.
But the thing is, going for a pure corruption/well/spectral in utility doesn’t grant you that much usefulness in actual dog fights.