Now, I understand that this is, in fact, Spring Training, and that he has gotten only 13 AB so far. We are dealing with the smallest of sample sizes. But as I was doing my daily A's website jumping, I came across this video about Sweeney doing blah blah blah.
Then I noticed a little something about different about Sweeney's swing. This little video is all I have, but it's interesting. It looks like he has raised his hands slightly to about shoulder level, maybe a little bit above.
In comparison, take a look at this video. His hands are just barely at the letters.
Everyone has always wondered if the power would ever come with this kid. It's always been there. But as people have pointed out, he's basically got a slap-style swing, the kind of swing you'd find on a player that's 5'8" with no power, not 6'4" and athletic as hell.
Now I'm no expert on hitting mechanics, and I wouldn't stake my reputation on this one little video. But I would assume, based on intuition, that you could get more power if you started with your hands higher and didn't slap at pitches. If he does figure it out, and ends up hitting ~20 HR a year, he might end up being one hell of a player. Just remember, he just turned 24. And he is hitting to the tune of .528/.600/.846 in those 13 AB.