That's very old in the tech industry; all people above that age need reading glasses and so on. That's for all devices with a screen if they don't use contacts.
…It is a future of computing, yes. Spatial Computing is in many ways very much a higher-end and more convenient form of  computing for a variety of use cases than non-spatial-computing platfomrs .
Replacing your Mac is deliberately ambiguous and left to be varied to user-to-user. It is not intended to necessarily mean COMPLETELY replace a Mac at all. That a straw-man takeaway from their marketing on your part. 
The Vision Pro is designed to replace using a prosumer Mac and iPad Pro for a variety of use cases its intrinisically can  as a spatial computing device and having several parities with such devices (Prosumer HDR performance/support, Automatically iPad app compatibility unless iPad devs opt-out, Apple Silicon on par with iPad Pro SKUs at time of launch, and so on).
For a Vision Pro to completely replace a Mac, it would need a OS as open and its APIs having full parity to be objective.