The issue with oblation is it has basically no impact compared to what its competing with and its not really a skill DRK ever needed.
I think we can all agree that the design idea behind Oblation is that its mean to be paired with TBN, basically all the time, and its a really weak cooldown on its own.
It seems to me the devs thought they were being clever with its design, as people complain about TBN not breaking so if we buffed it that would happen even more.
The issue becomes "when am I supposed to use this?". Oblation is the 4th best mitigation cooldown you can pair with TBN. For anything serious you're likely going to want Shadowall for the 30%, and if thats on cooldown you're going to go with Rampart, or more likely Dark Mind with its 60s cooldown. Especially in the current savage tier, Dark Mind really outshines Oblation in any place you'd want to use it on yourself for basically any tank mechanic. It has the same cooldown, but 20% is just so much more noticable than 10% even with two charges.
All that leaves Oblation for is for throwing it on someone for their protection. Which I mean, its okay at that. TBN is going to be doing the heavy lifting if its a non tank you're trying to save, 10% is rarely going to be the difference maker there.
10% mitigation isn't nothing, but its not a lot. Worth using but its not satisfying, and in most scenarios feels like it can be ignored entirely in favor of just using TBN. Either the hit is strong enough to oneshot them through TBN, or TBN is enough on its own to dull the hit and save your target, there is a very, very small window where its required to use both to save someone.
And if you're putting it on the other tank, and they use their own mitigation, you're likely going to just be over-mitigating for no reason. So its useful, but if you're using it, you're already in sub-optimal positions. This honestly just lead to me throwing it out randomly during downtime for no other reason than I can. Like I use it in the 2nd half of P3S to take the damage from those teeth, but its not like it makes that any more comfortable for me even, its just a button I can press that feels like its almost doing nothing on its own. I've never found myself in a situation where I'm thinking
"man I'm taking a lot of damage here, good thing I have a charge of Oblation"
Its a shame, it has a cool animation, and I love tank shields you can throw onto other players, I just wish it did more, and I wish it was a skill worth using without factoring in the existence of TBN