The value of OBP should vary where a player is in the lineup, b/c it's going to be more environmentally contingent than SA. Batting Galvis anywhere but 7th or 8th never made sense, at the bottom of the order SA has relatively more value b/c most pitchers are sure outs, reducing the value of getting on base v driving in runners.
If Freddy becomes more disciplined, that shouldn't hurt his power, not swinging at pitches you can't handle not only means you walk more often, it means you see better counts in many of your PA, it's easier to drive a ball looking for your pitch on a 2-1 count rather than protecting the plate on a 1-2 count after you swung at a slider in the dirt. This holds for most players (there's always an outlier or two), which is something to watch in Williams at Lehigh, Stairs was working on getting him to wait on pitches because he has the quick wrists to hold off to the last milli-second.
Not sure how much plate discipline is taught, instinctual or a product of swing/reaction time - some players may be able to see the spin on the ball? Some are able to keep their hands back, recognize the pitch and then react - some have long swings/slow reaction times and have to guess and swing.
It's not just a matter of power and pitchers respecting the hitter, some light hitters have BB% in the 8-12 range, some power hitters have low BB rates. Power helps because it encourages pitchers to nibble, but light hitters can also force the issue by deliberately fouling off strikes they can't handle (it's an art, Richie Ashburn may be the all time master).
All hitters, however, can learn to focus on their strengths and study pitchers and know what they'll throw to tempt the batter to chase, just laying off clearly unhittable pitches would help someone like Galvis. It takes more confidence to lay off the FB on the edge of the plate and hope for a good call. It takes a lot of vision and confidence to lay off a 2 strike breaking ball that you expect from film study will fall out of the strike zone.