It won’t work with the page excerpt, but you can write text directly into the slider in Exoplanet Pro.
To enable this in the customizer, go to ‘Home Page Settings’ > ‘Slider Settings’ and in the Choose how to build your slider content setting select Text Inputs.
Now in ‘Full Screen Slider/Hero Section’ you can write the Caption Sub Title text directly into the slider.
It will also work in the page editor slider settings in the Sub Title text area.