The best nuke nerf would be having the C4 weigh the barrels down, and reducing the barrels health.
This nerfs the tactic but doesn't nerf the heavy class itself.
Recon senses just need to be reset to where it was before it was buffed.
The complaints about invisibility and double barrel have almost completely gone away with the ADS patch, and people discovering that recon is an effective counter.
The issue with lights are their viability in competitive play.
It's an extremely high skill class to use.
Ranked mode has players maximizing strategies. This is why nukes, defib, heals, etc are so prevalent.
It would take a highly skilled team player to run light in a ranked mode that by it's nature and ours is filled with meta strategies to insure a win.
The light could use a few more team play gadgets, but it doesn't need a nerf.
Competitive gaming destroys enjoyable gameplay because the win is more important than the experience.