I think the font sizes are just fine. IMO, WP is really easy to navigate and understand and I think the styling and sizing of fonts is very effective.
No problems for my 56 year old mother (Icon) who came from a Blackberry, 57 year old dad (Icon) who came from an SG4 or 86 year old grandma (822) who came from an Android pone.
Maybe I am missing what you are saying, but I would say it sounds like you haven't really used WP very much.