You absolutely do not have to distribute VMs manually. This [0] is a tiny Python script run as a cron that migrates VMs in a Proxmox (also free) cluster according to CPU utilization. You could extend it for other parameters.

While I don’t personally have experience with more enterprise-y solutions like VMWare, I have to imagine they have more complete solutions already baked-in.

[0]: https://gitlab.com/tokalanz/proxmox-drs