I feel that squishing all three Destruction Staves into a single skill line limits a lot of the build fantasy that you can achieve, so here is my suggestion:

Turn the current Destruction Staff skill line into a World skill line labeled as "Destruction Magick", that way we can keep the skills around that don't have a place in the staves, and it would keep tthe debuffs relevant. Move the Destruction Staves into Flame Staff, Lightning (or Shock) Staff, and Frost Staff.

You could then take the passives from the Destruction Magick line and have them be passive for these skill lines, and then focus these staves into different styles of build. Flame could be a DoT build, or a Healing build (cauterizing wounds, warmth, etc.), Lightning could be AoE or Buff (speeding up allies, granting buffs), and Frost could obviously be a Direct Damage or Tanking set.

Separating them like this would help to distinguish their abilities, while also keeping the older skills around to provide their current functionality. I don't have many ideas for what the skills they have could be, but the general theme of them works out really well.