I feel like those who are selecting "all-rounders" have a much easier run of it as the bowling is a little easier when weighed against the batting learning curve currently. Think possibly in career mode, if you chose "All-Rounder" you shouldn't be able to earn skill points as easily as choosing a specific skill-set (Opening Bowler/Batsman for example) and perhaps your career progression should be weighted a little differently. Currently, I believe you earn points as quickly as a batter-only or a bowler-only, therefore you've got an easier chance of progressing quicker?
That's certainly my perception. Don't know how many "pure" batsman there are playing, but I'm willing to bet they're getting the game-rewards slower than the all-rounders are... which is a tad unrealistic, as it's infinitely more difficult to be an all-rounder, or it should be.
In a future edition of this game, it would be really neat if your performances dictated your abilities so you had no choice over what you wanted to be. If you're starting out at School or Club level, then you generally bowl and bat quite a bit for a while, certainly as a young'un to decide what you're good at. I reckon there's an opportunity for a "skill bar" approach to these early years in the career and once you fill up a certain obligatory requirement, the game asks you if you want to "specialize" in a specific area based on your results as a Bowler, or Batsman.
Then as you progress, you might suddenly start to get better at another vocation, therefore the game might prompt you again and so on... There's many examples of players starting out as one thing, but finding their way in another skill-set. Lots of batsman becoming bowlers, and vice-versa, certainly, in their early career years.