I would like to share that the host CPU usage in task manager does not show the CPU usage from guest machine level. You may refer https://blogs.msdn.microsoft.com/virtual_pc_guy/2008/02/28/hyper-v-virtual-machine-cpu-usage-and-task-manager/ for a better explanation.
To get the performance bottleneck, performonce monitor function is needed. A counter name Hyper-V Hypervisor Logical Processor(_Total)\% Total Runtime must be referred. According to https://docs.microsoft.com/en-us/windows-server/administration/performance-tuning/role/hyper-v-server/detecting-virtualized-environment-bottlenecks, if the Hyper-V Hypervisor Logical Processor(_Total)\% Total Runtime counter is over 90%, the host is overloaded. In this example, it is necessary to consider upgrade to a higher CPU spec host server to get a better CPU performance. Please refer below graph where the reported value from this particular counter is always exceed 90% as sample.
Also, the CPU usage reported from Hyper-v manager also reflect the usage as like above counter’s purpose.
In this example, this server CPU is overloading and is not enough to sustain the usage from the guest virtual machine.