It’s good to get these numbers out in the open. Steinberg is going in the right direction, but we as users definitely need to push the plugin vendors to reduce their slot usage!! UAD and Arturia are my biggest culprits, on average taking up between 2-4 slots per plugin. Whereas Waves uses only 2 no matter how many plugins you use.
I found a way of gaining a few extra slots as well. Drag and drop the plugin onto the Cb icon on desktop and you I always get extra slots over opening Cubase and then opening the project from the Hub. It seems that on my system the Hub takes 6 slots itself (after opening the hub and I see the free slots go down).