100% to this, most people over 40 that I have trained on Playbooks complained about font size. Increasing your browser font made the page not fit correctly. I wonder if it would be more awesome if you could drag that playbook OUT of your main HS screen so you can work on multiple monitors like most of us do. Then you could really make it large but see other contextual fields and activity that you might need to refer to, without affecting the HubSpot layouts by changing the zoom.