A lot of people use it. I for one use it because it is simple to manage, setting up shared storage is a breeze, live migration is super easy. I don't use any of the fancy NSX stuff and whatnot because I don't believe they add any value.

I was looking at Proxmox, but I kind of got lost in the documentation when it comes to shared storage and high-availability, meaning restarting VMs on another host if one host fails.

RedHat is just as expensive as VMware used to be, but it had less features, so it is not really an option.