Just like, calc the actual Roar's AP, slap that shit on Femto (might not even need to upscale if just facetanking that is higher).
It very much is like 0.01%. Honestly probably way less.
This thing is like what, 200m wide? 100m tall? And DS is what, 3-4cm thick?
Let's approximate, 100x200 ellipsoid, that's 16755160.82 cubic meters (obviously it isn't solid all the way through but ya get it), and the surface area is approximately 251327.41 square meters. Give or take.
Assuming 4cm, 200cm for DS, 90 degree slash, we're getting about 125663.71cm3 of cut tissue at most, and the total surface area covered by the swing is approximately 2056.64cm2. Which is like, 0.00000075% and 0.0082% respectively, so like.
To put that into human values, DS would be like a razor blade but covering even less area total.
Obviously those numbers ain't exact but the things heart is just an extremely small fraction of it for some reason, like tbh it should be larger than a building given its scope.