I mean the cabbie is just Caine in the game files. As far as we are concerned they are just a vampire who's above it all, so above in fact that they are both in the background and behind everything that happened. All we know about them is that they are interested to see how a microcosm of the modern nights reacts to the promise of absolute power.
Short answer is that everyone failed. The Camarilla's doctrine did not prevent the prince from angling for that power, the Sabbat was too weak to defeat the Camarilla, and the Anarchs were too disunited to play at all. Each faction failed at their own premise. Even Jack, the red herring, ends up being caught up in his own politics. The only reason you had a conversation with the cabbie is because you were resourceful enough to insert yourself in the plot. Or because you were chosen as a tool from the start. Or both. Maybe you were just a licker at first, but then you succeed in serving LaCroix in Santa Monica and the warehouse, so you become an useful foil to all the experienced vampire lords of Los Angeles.
The only in-game reason why the cabbie would be Caine is the assumption that the PC's generation is out of whack or, rather, that they somehow became of higher generation in-between attempting to dominate Therese, being dominated by LaCroix, and then resisting LaCroix's final domination. But given that this is a story and character driven world we have tons of leeway to work here. It doesn't take Caine to empower the PC. It could have been some other would be god lower than Caine. And it doesn't take the PC to have been empowered - they could always have been of a lower gen, coming into their own over their ordeal. Or maybe the storyteller decided this isn't a generation thing, and the PC was of lower willpower before. Hell, the number of bloodpoints we have is more likely to be a concession to gameplay than an all important plot point.
C'mon, Ravnos doing his crazy shit and the Technocracy busting his arse (and then making their damned best to make everyone memory hole it) is just a guilty pleasure.
I don't know man, it's probably just me but it's hard to care about a world when power levels get that far. Plus, it could be that warhammer fantasy made me wary of stories where the writers go 'hey our world is set in a supposed near apocalypse, lets end it finally'. I rather like the gehenna in the modern interpretation. It solves both the power curve and the apocalypse issue.