No to fireball leaving a surface. Aside from fireball already being too powerful of a spell, it just wouldn't set the ground on fire. Have you ever tried making a campfire? If you hold up a lighter to wood, the twig/log doesn't immediately catch on fire. It takes time and care to actually catch most things on fire, even more so for (wet) grass, dirt, stone - all the various types of surfaces in BG3.
VERY LIMITED surface usage could be cool in BG3, but it has to be done well. The consequences of each surface should be considered and balanced with the rest of 5e mechanics.
