In order to allow ESXi to control CPU power-saving features, set power management in the BIOS to “OS Controlled Mode”. Even if you don’t intend to use these power-saving features, ESXi
provides a convenient way to manage them.
High performance power policy will provide the full hardware performance.
To change to "OS Controlled" you need to reboot the host and configure the setting in the BIOS.
CPU contention could be due to a number of factors. Some of them include, high over commitment, over population of VMs on a host or large virtual machines. I suggest to have a look on that as well.