I actually get why they went with the Borg. I'm... disappointed, but I get it. The Borg are Picard's villain; they're the villain that's personal for him, on an intimate and ultimate level. In that sense, they're a perfect and totally appropriate choice.
But...
It would still give a greater sense of narrative realism if they'd chosen something equally powerful but indifferent to the Main Protagonist. That's really what gave the Borg their original narrative power: it didn't care. Not 'they' -- it. It was a monolith of a species. Unrelatable. That got cast by the way pretty quickly, of course. There was probably no choice, since in order to make them an active and ongoing threat, they had to be retconned into assimilators of organic life. It was their increasingly humanized portrayal that robbed them of their gravitas.