The font on the dev site is much harder for me to read. The use of several different fonts and the underlining creates visual clutter.

Fonts with serifs (like the one on the regular site) bind letters together into words and play a significant role in the neurophysiology of reading. Good typography and page design developed over centuries and are functional in many ways. Look at the page layout of an elegant well-printed book.

In general sans serif fonts work best for road signs and tabloid headlines, but not for longer blocks of text that people need to be able to scan with quick recognition. (Some research shows that some dyslexics do better with non-serifed fonts. But most people read sans serif with lower comprehension and speed.)

I suggest that the new site might have an option for an alternative/large type view, but that otherwise using fewer different fonts and sizes will maintain legibility.