It’s good to remind that the CPU meter in FL Studio doesn’t show actual CPU usage but a “buffer fill” and % of it running out.
Different metrics - The FL Studio CPU meter measures how quickly each audio-buffer is filled. Specifically - (Time taken to fill the buffer / Buffer length). 50% means the audio for the buffer was generated in half the time available. On the other hand, the Operating System CPU meter measures overall CPU ’ utilization '. Utilization is the percentage of processing-units on the CPU in use. Specifically - (Processing-slots in use / Processing-slots available). 50% means half the processing units were in use. So, utilization is about processing capacity not how quickly it is processing a given task , such as the FL Studio audio. Put simply, FL Studio’s meter measures time (processing speed), the Operating System measures capacity (processing slots in use) . The two measures are not the same, even if they are both reported in percent! But wait, there’s more: time-scales and logic .
There’s more detailed explanation: https://www.image-line.com/fl-studio-learning/fl-studio-online-manual/html/toolbar_panels.htm#Multi-core_Processing
But back to Vital - I personally don’t see a huge difference when all effects are in use VS when they aren’t, but I believe it heavily depends on hardware configuration. Also good to mention that wavetable synths generally need more processing power than your regular synths.
Anyway you can make Vital use less processing power simply by setting it’s oversampling to DRAFT in ADVANCED tab, that should allow you to use more instances.
Depending on your DAW you can also set audio buffer to be bigger for a cost of bigger delay (can be annoying in case you’re using midi devices) or by simply changing sample rate of the whole project to lower & then before exporting setting it back up (treat it as a last resort option).
FL Studio allows you to also use “TOOLS >> MACROS >> Switch smart disable for all plugins” which will have a huge impact for you in case when you use a lot of plugins.