If we are talking first round or first couple rounds, you will see lots of pitching in most any year. Other than that it is all about talent, more than about position.
Last year I believe the first three picks were shortstops. This was actually very unusual. And yes, there have been first baseman drafted early out of HS.. Prince Fielder, Eric Hosmer, Freddie Freeman, off the top of my mind. Yes there have been HS catchers also drafted early. Austin Hedges, Joey Mauer, and several others. Mauer was actually the first over all pick.
Not sure about MLB catchers being weak behind the plate. Some better than others, but that is not where you want someone that can't catch. Actually I think some of today's catchers are among the best ever defensively. The Cardinals catcher might be one of the best ever.