There are drift dives and drift dives. It's not unusual, here in the Sound, to do a dive centered around slack at a current-sensitive site. You drift gently one way, and when the current reverses, you drift gently back. Those dives are not difficult for beginners, but the divers are highly dependent on a boat captain who can time the slack properly.
High velocity drift dives, especially along walls, are a different animal. When I did my trip to Bunaken, I had about 150 dives or so under my belt, and I got caught unawares a couple of times by up and down currents, and it was highly unnerving. It did help that I knew my equipment well and that managing my buoyancy had become a very fluid thing.
To me, one of the big issues with strong currents is diver separation. If you aren't pretty vigilant, it's very easy to be swept into an area of faster water, and get separated from your buddy or your group. (This is also very true with up and downwellings, which may be quite localized.) One of the things newer divers tend not to be very good at at all is situational awareness. They don't have the bandwidth to manage their own gear and their dive, sightsee, AND remain constantly aware of where their buddy/team is and what the water is doing. It's like asking a new driver to juggle a cup of coffee and a cell phone while shifting gears -- ten years later, it's easy
You're right that you can't learn how to dive strong currents until you do it, and that education, though it can help give you tools, can't replace experience. But it is a good idea to have a strong sense of where you are as a diver, and how much challenge or stress you can manage in stride, before you start expanding your horizons in an aggressive way.
And, BTW, I'm not at all sure I would be real happy diving the Galapagos, and I've done a lot of diving in a lot of places. When somebody who handles currents well describes a place as difficult or advanced, it's a good idea to listen to them!