This is from UESP
https://en.uesp.net/wiki/Skyrim:Flames :"In the original Skyrim with no DLC, Flames was worth 20 XP/s, on par with Frostbite and Sparks for XP per Magicka point spent. Dragonborn knocked this down to 14 XP/s, probably unintentionally, making it much less favorable for XP gain."
I think Dragonborn also makes more edits to the Flames spell. The chance is high they are wild edits.