About 43 million ipads in 2018: https://www.lifewire.com/how-many-ipads-sold-1994296
Chromebook is estimated to be under 11 million: https://www.computerworld.com/article/2476098/huge-chromeboo...
I couldn’t find 2018 unit estimates for the surfsce, but in 2017 the estimate was about 3 million: https://www.pcworld.com/article/3254235/microsofts-surface-p...
Surface revenue in 2018 was about 5 billion. Apple’s ipad revenue was a bit under 20 billion. And these surface numbers are for everything in the surface line, not just pros.
A more likely explanation for lower ipad sales is that they last a long time. My ipad air 2 from 2014 still runs beautifully and gets security and software updates. But in any case ipad sales dwarf the surface and and chromebook sales combined.