These are pretty different vendors fwiw.
• Crossplane is more of a multicloud control plane play though you could build a developer platform on top of it. Significant work I think to build on crossplane.
• Humanitec internal developer platform.
• Check out
Loft.sh for an internal developer platform, as well, that is Kubernetes focused. They are growing very quickly and have some pretty strong customers and are built on top of
vcluster, which is a super cost-efficient OSS project.
• I don't know enough about Kubevella to comment but it seems tighter on
software/application delivery than a developer platform.
So I would start by asking what exactly/how much you want to build, whether you want a commercial offering or OSS, how far you want a developer platform to extend, what you have already (CI/CD through Jenkins or Gitlab or do you want your developer platform to cover this?)
Consideration is probably less about observability for the developer platforms (Humanitec, Loft) and maybe more for the PaaS-ish plays (Kubevella, Crossplane.)