For VM management I agree with you. For other things cockpit is mostly fine.

Cockpit is not ever going to be as good as using the underlying tools it integrates with, but it is still pretty nice for what it is and I like having it.

I haven't really kept up with this, but last I heard virt-manager was deprecated (on RHEL at least) in favor of just Cockpit, hence the comparison.

Cockpit is definitely nice, but it still feels pretty incomplete compared to virt-manager.

virt-manager appears to still be developed, though, just without the same blessing/level of support from Red Hat.

Sadly true: deprecated in RHEL 8, removed in RHEL 9. Although we'll continue to develop and ship virt-manager in EPEL so the majority of people will still easily be able to install it.

virt-manager is just a shim on top of libvirt same as cockpit's VM component. So there really isn't any excuse on that front. Although your comparing a tool built as a competitor to something like vmware workstation/virtualbox against a general purpose machine mgmt tool that happens to be able to do some VM mgmt as well.

PS: I think both are good, but I too use virt-manager for all my VM twitting because nothing else on linux is both as feature complete for qemu/KVM while also avoiding having to read the manual just to adjust some VM parameter.