Amazon Neptune isn't that great - discussions regarding vertical scaling
medium.com
medium.com
For example at SSENSE we leverage Kubernetes but some pieces of infrastructure (actually quite a few) still live in AWS. Bringing up new environments of our Kubernetes resources is easy be it deployed or just local. But the AWS parts at least in our experience are encumbered by issues ranging from just slowness of setup, to permissions issues, Region/Zone issues, dealing with the complexity of another toolchain apart from Kubernetes (e.g. terraform), needing coordination with the Ops team which can lead to occasional hard blocks, and so on. All to say that having a database that is flexible to run where you want is awesome IMO.
Still, IMO their design is outdated for something built in 2017.