If the sprights were more populous and not the slaves of Morgause, what exactly would they excel at, compared to the rest of Gaia’s peoples? What type of jobs and Magic’s would they do well in?
That's a good question, and I think there would be multiple answers depending on where the sprights are. Because of their small size, they're part of the group known as "wee folk" which is comprised of gnomes, pixies, abatwa, and of course sprights. Wee folk kind of have their own little culture and ecosystem separate from the larger species.
If gnomes are the "humans of wee folk", then sprights were like the elves. Physically weaker than gnomes, but better at learning a wider variety of spells. Plus, female sprights can fly which is a major boon. Before Titania's conquests, sprights had largely dominated among the wee folk, especially in the southern mountains before the volcano erupted.
Basically they were the biggest fish in their little pond...then they suddenly got thrown in to an ocean of sharks.
If such tragedy hadn't befallen them, I think sprights would have filled niches that other wee folk currently do. They would make good spies, dentists, surgeons, tailors, and messengers especially. They would basically be smarter, stronger, and overall superior versions of pixies. Pixies, after all, were Titania's (somewhat failed) attempt to replace sprights. Unfortunately pixies have naturally low IQs and bad temperaments. Sprights do not have these issues, they're quite intelligent and reasonable.
So I think if sprights made a comeback, they would quickly lead to some kind of mass pixie-displacement in society. I could see pixies eventually becoming some kind of lower, subservient class to the sprights, the way that kobolds are to the drau, the drau are to the adhene, and the adhene are to elves. They'd just slide right into the societal hierarchy.