First of all, Gig Performer is showing only the CPU cycles used by the audio processing. That’s completely different from overall CPU usage which you would see using the Windows Task Manager (say)
Secondly, SampleTank is consuming an absurd amount of CPU cycles even when no audio is being produced. A well-behaved plugin should barely have any “audio processing” CPU activity when there’s no audio being produced.
(See movie for example, using DS Thorn plugin, watch the (slightly lagging) meter as the audio comes and goes)