Hey Tom, I was using Simple CSS today and I had this insight of suggestion.
On Simple CSS screen we have three postbox (GeneratePress, Customizer and Tips). I suggest to check to see if GP is installed before printing GeneratePress postbox.
I think that this information is irrelevant if you are already using GeneratePress (or any child).
For some reason wp_get_theme()->template doesn’t always = generatepress in all cases. Super strange but something I struggled with a couple years back.
Good to know this strange stuff. Your solution is indeed better, since GP Version is already in memory and wp_get_theme return full object that we don’t need.