For me that is more few Ideas they tried but that either didn't or they never really comitted to.
The daylight thing is imo kind of dumb, from an inuiverse perspective.
His powers aren't that developed, and sofar not really srong enough to do anything the others couldn't do with tech.
His civilain life and support cast is pretty underdeveloped, and you could do that with most of the others to.
Fot the evil immortal there is also Damian with Ras, and Ras is just a way better developed character than Gnomeon.
And I wouldn't really call him a staple member of the Outsiders (he was on that team for what? 20 issues or so?), and the Outsiders are anyway more a B or C list team, not on the level of Titans or Young Justice.