For example, encryption at rest or in transit essentially eliminates attack vectors. The possible attack avenues necessarily shift as a result, but only because an avenue was blocked.

That's very different from e.g. adding a layer of protection around something insecure, where the insecure thing remains insecure inside the protection, which I think is what the other commenter was imagining.

Similarly, memory safe languages (including most GC languages, not just a certain language beginning with R) eliminate entire classes of security hole. Again, the possible attack vectors necessarily "shift", but that doesn't capture the fact that you've entirely eliminated a class of attacks.

The same goes for eliminating unnecessary services, firewall holes, etc.

None of these are specifically trying to "shift it to something to something that is more difficult to compromise." They're entirely blocking attack vectors, and the strength or weakness of other parts of the system aren't really a factor.