My vmware experience is a couple of years mostly as an internal user of a cluster totalling about 1000 VMs, not using any advanced features like FT/vSAN/NSX. I'

My vmware experience is a couple of years mostly as an internal user of a cluster totalling about 1000 VMs, not using any advanced features like FT/vSAN/NSX. I've also developed a KVM-based IaaS platform. I think your concerns are justified (and is it possible they are just applying existing knowledge and experience without considering your requirements properly?) The vSphere Web Interface drives me insane. It is slow, does not do background polling for updates and ends your session after 2 hours (by default). ESXi is fine as a hypervisor but not having a Linux host (as with Xen/KVM) to do things like advanced networking/firewalling/hardware troubleshooting/stat scraping is quite frustrating. You're mostly limited by the vSphere(/NSX/etc) APIs. DevOps tooling (e.g. packer, terraform, ansible) treat it like a second or third class citizen, if at all. I think you need to look at the applications' architectures and work backwards from there.