The spells are more "tools", they are not intended to be weapons. Used for environmental puzzle solving, and can yes, add to combat. Stun an enemy with electricity, set a explosive on fire and throw it at an enemy. But, also keep in mind, this is rather bare bones, it's still a work in progress. As for performance, there's a bug in the build of UE4 the demo runs on that hindered performance. Epic have already fixed this problem, and we are moving to the newest update soon. But, it wasn't possible to update before the demo release, as updating would cause issues that would need to be fixed before it could release. But, performance will definitely be improved in future builds.