Akima for Yield Curve Interpolation ?

On my test of yield curve interpolations, focusing on parallel delta versus sequential delta, Akima is the worst of the lot. I am not sure why this interpolation is still popular when most alternatives seem much better. Hyman presented some of the issues with Akima in his paper in 1983.

In the following graph, a higher value is a higher parallel-vs-sequential difference.

That plus the Hagan-West example of a tricky curve looks a bit convoluted with it (although it does not have any negative forward).

I have used Quantlib implementation, those results make me wonder if there is not something wrong with the boundaries.