When would you use Twist of Fate oder Divine Insight? Instant MB = Instant Damage and orb generation. Instant casts are one the most important things in the current (pvp) meta game. And ToF has very little uptime in PVP.
Yes, then why doesn't arcane torrent gives SPs an orb? That would make the race a lot more attractive.
After all these years of roleplaying/flavour weighing in WoW, I have yet to find a proper attraction for Blood Elf Shadow Priests. Blood Elves sure try to be in touch with the Light, but there is zero connection to the Shadow.
Actually BE's background is pretty rogue oriented, and SP have some similarities with rogues, both are from the shadows(though the actual game play of Priests needs to be adjusted in this regard) so I wouldn't say there is zero connection between them. And I am talking about gameplay not lore.