DRK changes that would make it really fun to play

[Archwizard]

Oblation mainly exists because of how TBN works right now as if you added mitigation to TBN it would make it harder to break which is counterproductive, oblation even looks like "enhanced TBN" from the animation

Even then, they could have directly upgraded it multiple ways without making Oblation OR increasing the difficulty toward getting Dark Arts. Off the top of my head:

• Reducing the barrier potency of TBN to 20% but adding on a raw mitigation effect over it to compensate, which would continue even when the barrier is consumed.
• Extending the duration of TBN and causing a raw mitigation effect on its target for the remaining duration whenever the barrier is consumed early.
• Causing TBN to also grant a healing effect of some variety, like Bloodbath or restoring a fraction of damage absorbed.
• Causing Edge and Flood to gain Drain effects or Cure potency when used under Dark Arts.
• Just giving TBN a second charge like Sheltron, and letting you store two Dark Arts at once or spend Dark Arts on TBN.

The only justification for adding a double-weave on our basic mitigation and contributing to button bloat with an excessively weak tool, is in attempting to balance out TBN's awkward position compared to other on-demands as a tool usable 67% more often.

Off the top of my head, I think they should introduce Oblation at like, way earlier levels (maybe 45 alongside Dark Mind) to address the 'DRK is squishy until TBN' issue, then at it's current level, trait upgrade it to have 2 charges

At that point it seems more likely they would just rework Dark Mind, fusing the 10% raw mitigation onto it with a bonus to magic resist, a la Camouflage.
The two share the same CD after all, Dark Mind is already decried for being niche, and it would save a button in the long run. Maybe trait an extra charge onto Dark Mind at the level Oblation is normally introduced. Whether it gains the ability to cast on allies at that point or earlier is up for debate.

Or, they could solve that issue by adding a downgrade to TBN at lower levels (return Shadowskin?), that upgrades into TBN at 70.
... Of course, they would need to address the MP economy of TBN if they wanted to make a downgrade to it without turning TBN itself into the downgrade. Can't have an MP-based mitigation without giving Dark Arts to compensate for the DPS cost, and as Rithy pointed out, any upgrade that makes it harder to get Dark Arts is counterproductive.