Cook is on record in 2012 as using an iPad for 80% of his work, which mostly involves communication activities such as making decisions, responding to emails, and viewing documents. With how Apple has since then differentiated iPadOS and released accessories to make the iPad more laptop like, I'd guess that percentage has only increased.

The iPad was launched in 2010 and seen as a device to play around with - a big ipod. Two years later they were in the midst of the big push for using iPads for business, in hospitals, in cafes to replace PoS, in factories, etc. So you say the CEO of Apple uses it for work, if it's good enough for him it's good enough for you. I highly doubt he doesn't use an actual computer.