In terms of features, I imagine they are about the same. Here is why I think this. Maxima's function organization seems to follow and refers to the NIST Digital

In terms of features, I imagine they are about the same. Here is why I think this. Maxima's function organization seems to follow and refers to the NIST Digital Library of Mathematical Functions https://dlmf.nist.gov/ https://dlmf.nist.gov/ Mathematica and Sympy also seem to follow this organization. My take: I blame compatibility on the NIST Digital Library of Mathematical Functions.