Hello,

Currently, the font-weight is set to be 400 what means “regular” This font does not assume thinner variant http://prntscr.com/njx4qw

If you want to have one font-weight on desktop and other for mobile, copy the layer, set different font-weight
https://www.themepunch.com/revslider-doc/layer-settings/

and hide the layer on devices accordingly https://www.themepunch.com/revslider-doc/layer-mobile-visibility/

Bes