I eventually rethought whether Childhood's End had a happy ending. It seemed as likely that the human race was eaten as that it transcended.

Some other candidates for discussion: The Cosmic Rape by Theodore Sturgeon and The Persistence of Vision by John Varley.

But there may be a substantial issue here: once one has that sort of ending everything else in the story may feel trivial in comparison.

There's actually some explicit discussion of this in Worm's epilogue. That story had a relentless ramp of challenges always getting larger and larger until they were as large as possible (and then the story ended), but it was more of nireg n artngvir fvathynevgl naq gura yvir n abezny yvsr, vafgrnq bs oevat nebhaq n cbfvgvir fvathynevgl naq gura yvir n fgenatr yvsr.

Haven't read it, putting it on my list now.

Upon some reflection, the reason I liked Luminosity less on second reading seems to be at least partly that the protagonist started as a relative underdog (sympathetic) and ended up as dominant authority, one effective in their dominance to an oppressive degree, enforcing her ideas on everything and everyone. This moved me out of "yay, rationalist fiction, let's get into it from the pov of the protagonist" into a third person view... from which I started noticing how freakin' obnoxious rationalist!Bella is. Poor Edward.