Already tried using vmrc, it is better but still not satisfied user. It is not problem only with keyboard it also effects mouse.
If the end user does not have direct remote access to his/her VM through native remote access technologies like RDP or SSH and are therefore forced to use a VM console, then there's really not a whole lot you can do about it if they're forced to do so through a RDP session. User experience can be improved over a PCoIP-based Horizon desktop in some cases, but you're still not going to get performance like you would when accessing VMRC natively.
I am a freelance developer and I've many VMs in my homelab. I used to have access to VM Remote Console through VMWare Workstation since you don't need to configure anything on client side just connect to ESXi server, that's it. However, time to time weird keyboard problems occur in remote console. If you're Turkish user like me and frequently switch between US and TR keyboards then you may get into such trouble. That's why I switched to RDP.
However, if you're connecting to customer networks via VPN and VPN does not allow even LAN access then remote console is the only option.
I also experienced KVM (Proxmox in specific) and SPICE client. The user experience is much better imho. I wish ESXi supports RDP like VirtualBox does.