I understand where you're coming from but I think you're applying the wrong perspective. I suspect what's giving you that reaction is the feeling that a prestige class should be a class that enables a specialized or unusual build rather than a straight power upgrade, and I agree with that.
The thing to understand here is that "hybrid divine/arcane necromancer" is already a specialized and unusual build, and one that's non-viable without a prestige class to support it. The nature of the build required to get in already makes it something unusual, so all the class really has to do is bring it up to a level of functionality that matches up to a straight-classed cleric-necro or wizard-necro.
That said, it would be nice to see some of the features build up a synergy between the two classes - substituting a holy symbol for arcane somatic components is neat, but I feel like there's more that could be done with blending the two forms of magic.