I didn't watch him hit all 45 bombs last year, but based on the numbers, I think I have a fair bit of confidence that he has great power. I know people are generally more suspicious of defensive numbers for whatever reason, but at a certain point they, coupled with the consensus around the game that seems to have him as a fairly mediocre defender (although there were other factors at play, the fact that the only team willing to offer him a long-term deal plans to use him primarily as a DH seems noteworthy), are worth something, right? Not to denigrate the value of anyone's eyeballs, but the idea that you can't know anything about a player's defensive skill, and have to be purely agnostic on the subject, until you, personally, have watched them extensively seems...a bit preposterous to me.
Perhaps more to the point, all of us have had the opportunity to watch our current group of outfielders at work, and I for one feel no urgency to break up what should be one of the better defensive outfields in the majors on account of JDM. I expect we'll see him start from time to time to rest one of the starting three, but if it's any more than that, it means that one of the Beni/JBJ/Betts trinity has gotten hurt or their playing time has been cut for some reason, so for that reason alone, I certainly hope we don't see too much of him in the field. As someone else said, he was signed to hit, and I'm excited as hell to see him hit...not terribly concerned about the rest.