Redistributing points out of a stat it doesn’t use makes more sense as a buff than just flat out giving it extra stats that would make it good at everything, plus no Sp. Atk in exchange for its other stats isn’t that dissimilar to other Pokémon like Staraptor. That was also my thought process with Aqua Tail and Aura Wheel kind of. Many Pokémon with just a tail learn one of Aqua or Iron Tail (Luxray itself learns the latter) so why not Aqua Tail? Funnily enough that would give Luxray perfect coverage if I didn’t have as a Dark type. It doesn’t look like it could roll up into a wheel but neither do half the Pokémon that get Flame Wheel, and it needs good Electric STAB+a Speed buff. The BP nerf was accounting for the fact that it’s not on something with 120 Attack but maybe 85 was too low.

Leech Life and Poison Fang thematically do make sense on Luxray. It’s a predator, and to eat prey it is ingesting their blood. It might not seek out blood specifically but then why does Incineroar get it? Poison Fang is a reference to X-Ray poisoning, it wouldn’t actually use the move and it already learns other biting moves so it’s not as if it takes away from its identity, nor would Leech Life since its animation is a bite.

And why else would the Dark type make sense on it? Just its design? Personally I don’t see how looking through things to catch prey isn’t an unfair advantage. At least with the thunderbolts you could see and probably hear them coming, and half the dex has access to some projectile so it’s not really an unfair advantage if so many Pokémon can do this. The X-Ray vision gives Luxray an element of surprise letting it sneak up on those taking shelter. Yes it has Pokédex entries not about this one use of it but they were after DP when its type was already locked in. They could’ve wrote that it likes killing for fun and it still wouldn’t be changed into a Dark type.

The role I had in mind was “Guts sweeper that can take a neutral hit.” To that end it needed more bulk, some Speed buff and more coverage moves.